I was under the impression you could use valet parking at all the hotels, not just the deluxes.
However, if you're going to drive to the Poly/GF, you may as well drive straight to the park and park down the front in the disabled section - well, Epcot anyway. MK you still have to get across the lake, whether you go by monorail or ferry.
I found the problem with parking at GF and Poly and going to the park after an evening ADR was that either we were last stop round the monorail there and one stop back, or first stop there and last stop back. At least if you do the monorail to MK from the car park, you can get the direct monorail there and back and not have to go on the ring via all the hotels.