No amount of parking can satisfy the demand for RER type frequent rail service, especially when fares are fully integrated with local transit. GO will have to move away from the park & ride model and towards the feeder bus model that's been serving the subway for generations. That means that YRT has to learn from its neighbours and significantly increase service over the rest of the decade.
Agreed, but that's another reason why having stations closer together makes sense. If you have a station at almost every concession road (~2km apart), running local transit service on the roads would allow more local routes to more directly intersect with stations. When stations are 4+ km apart, the amount of deviation the local routes need to take, and by consequence the amount of time a transit user spends on a bus before even arriving at the station, increases substantially.
If you have a layered express/local pattern, you can increase accessibility while not substantially increasing trip times. For example, on the Lakeshore West corridor:
Route 1: Local Union to Oakville, terminate at Oakville
Route 2: Express Union to Oakville, local Oakville to West Harbour, terminate at West Harbour
Route 3: Express Union to West Harbour (stop at Burlington & Oakville), local to Niagara Falls
With this pattern, you could add infill stations at Park Lawn, Lorne Park, Ford, Dorval, and Walkers without substantially impacting travel times for most people on the corridor.