Since you are a local resident as myself, there are 2 solutions: more parking structures and more buses or trams. Disney could discourage park hopping to alleviate traffic to the third park, but they need to have a full day park instead of the DCA fiasco.
As for the third theme park, that would be beyond awesome and there is definitely a market for that. I just think that Disney's options are out of the Anaheim Resort Area and maybe somewhere else in SoCal.
But Disney does have the capital and tech to make changes. Just a question of if Anaheim and CA will agree to them.
You'll never get guests to the parks via train. A special Disneyland bus would be great. There's a local LADOT bus I've seen in Downtown LA with "Disneyland" on it's front display. Why not adopt an LAX Flyaway system? Pick a few major spots in the cities, airports, Union Station, Hollywood & Highland, Universal Red-Line Metro Station and offer an hourly service for a nominal price. (Price point as to be lower than $30 for 4 people)
Or figure out a dynamic price structure for parking. $20/vehicle with 1 guest. $15/vehicle with 2 guests. $10/vehicle for 3 or more.
Regardless of a new park or attraction, it's not about getting guests from the parking lot to the attraction/park, it's about getting the guests from the 5 Freeway to the parking lot.
As for transportation. It will always be cars based in S.CA. Train culture doesn't exist here and probably wont for the forseeable future. Trains are only used by daily commuters to and from work to avoid LA traffic. Outside of LA traffic is actually very smooth so cars will always be the preferred mode of transport. The only realistic option imo is to build another parking structure in the lot directly south of frontier tower and west of paradise pier hotel. Cars can then exit up west street through disney way which is how they currently exit from mickey and friends parking or through katella which is a large street and could easily handle the extra traffic. Also theres a parking lot north of the garden walk that could be used too. Anyway I hope they can find a way because disneyland definitely has the clientele to support a third gate.
Disneyland suffers from the same land lock that USF does. The only way they will be able to add new attractions to Disneyland is cannibalize the park to do it. I am not so sure that is a real smart move for Disney since removing fairly new attractions to add new ones really doesn't seem to follow their game plan, but hey...look what they did with CA, right?
The single rider parking "fine" is absurd. I guarantee they loose money in the short and long run with that move, end of story. There really are only two answers to this challenge and they are build up or out. Either build parking parking garages like USF did or buy some more of that golden dirt that is Cali to pave a new parking lot.
Of course, there is always the hidden third option of offering another level of pass with parking as a perk with an increased pass cost, but the new passes have already been boosted a great deal, so I don't really see that as a good option either.
I am glad I live in Orlando where the Epcot parking lot is big enough to put a Disneyland or two in!
Ultimately Disney might have to make their monorail a tool and not a toy. If they can't depend on the city to connect to public transtit and spread out parking garages, Disney might have to do that themselve. I know there's the somewhat "historic" route, but the monorail line should be expanded there to connect new distant garages that could be city blocks away. Plus, if there is ever a third gate, the monorail should stop at all three parks and actually stop between Disneyland Hotel and Paradise Pier Hotel. Who knows, maybe at Disneyland they can bring back the PeopleMover in a real world application. Despite it's small size, it still needs to move large amounts of people around quickly and there is only so much walking and courtesy parking trams can do.
As to more mass transit, the OC Register reported that ART (Anaheim resort transit), OCTA and Santa Ana is looking at building a streetcar that will link up with Santa Ana and Garden Grove and possibly beyond.
But short-term moves, such as the two I described, could buy Disney some time and make these long-term fixes even more effective. (Interesting that Disney this morning posted a message to its AP Facebook page, encouraging annual passholders to carpool to the park.) Disneyland needs multiple solutions to solve this problem.
They can build two new parking structures in the short term. At the existing Mickey and Friends parking structure, add a second structure across from the tram loading area. Build the second parking structure off of Disney Way, across the street from Garden Walk, which will directly serve the third park or be the new CM parking lot.
If these parking structures are still not enough, many new parking structures can be built at the Downtown Disney short term lots.
To get people to their destinations, Disney should look into building automated electric trains on Disney property. A train route can leave from Mickey and Friends, through the Disneyland Resort Esplanade (over or under ground) (first stop at Disneyland/DCA), and along the east side of DCA (second stop at south/east of DCA). To save on cost by not having the train cross the intersection of Katella and Harbor Blvd, the city of Anaheim can contruct a pedestrian overpass to the third park. The train can climb to a second floor level so the guests can easily walk to the third park.
Guests who park at the Disney Way parking lot can walk directly to Disneyland or the Third Park. Perhaps additional overpasses should be contructed to ease the commute.
Guests who park at the Downtown Disney parking lots can walk to the esplanade to board the train to reach the third park. Or the train route can be extended from DCA to the south lot as the third stop.
This is my suggestion. Enjoy!!!
They could have easily run an additional monorail line (not connected to the current route) down that strip of land across Disney Way and feed it right up the side of DCA into the esplanade. Anyone wanting to walk to the resort still can, but I'd recommend a pedestrian bridge over Harbor Blvd. And the other side could have had a tram system that feeds right into the third park. Just a thought.
What's the length of track at WDW for peoplemover and how many can it accommodate per hour? That would be an interesting use of that attraction. Continuous loading, but I can see breakdown being an issue with multiple trains stopped on the raised track.
As for current options, the best option for a whole new park would seem to be the Toy Story parking lot, but we've already been through the logistical and spatial problems arising from that scenario. Perhaps not a full theme park but a lesser sized water park would be better suited for expansion? I've always been curious as to why Disney has never put a water park in the So Cal area seeing as their is very little competition in the market. Especially with Wild Rivers closing down recently.
I've never been a fan of Toon Town and I've always thought that if Disneyland was to ever do a major renovation the best option would be to get rid of toon town and do a major expansion of Fantasyland. Similar to what Magic Kingdom in Orlando is currently doing.
Frontierland always seemed a little small and odd to me. There is really only the shooting gallery, The Golden Horseshoe, and BTM to offer any kind of "theme" to the whole land in general. It never felt like a whole cohesive land to me. I know there is the petting zoo in the back but, seriously, who has actually spent any extended amount of time there? Getting rid of it and doing a major expansion of the land seems like a good idea. They may even be able to alter the river a bit and expand to the west. But what other major attractions could go into Frontierland?
Anyways, I'm ranting now but just wanted to give my input.