I don't know if this helps, but there are a few hotels and timeshare resorts which offer free (limited) shuttle services to the parks. The problem is that usually, they only offer it to either the Disney parks or the Universal/Sea World parks. Perhaps someone with a Florida
AAA book (American Automobile Association - a membership group) could look to see which Orlando area hotels advertise free shuttles to ALL the parks.
There's another thread that may be worth your time to read,
Do any time share resort have FREE shuttles to parks? The Fairfield resort mentioned is located in Kissimmee, just off Rte. 192, east of Disney. The rooms all offer at least a mini-kitchen and it's within a rather long walking distance of a Cracker Barrel restaurant and a couple others. This would be much less convenient to shopping, restaurants and mini-golf than a hotel located directly on I-Drive.
The "codes" (discounts for Disney hotels) mentioned above may be found online at
Mousesavers.com Depending on when you are planning to visit, these may be very useful... or not at all.
The I-Drive area (especially near the Convention Center and south) is a good home base area if you plan to visit a variety of attractions. The area of I-Drive near Wet-N-Wild is less pleasant, older, more congested, with some cheaper, more rundown hotels. Do some online searching and find a place near or below the Convention Center and you'd do fine!
The idea of staying at a Disney hotel for part of your stay and at a Universal hotel for the rest is a good one... IF you don't mind paying theme park & hotel prices for all your meals. It's certainly more convenient than dealing with offsite without a car. But if that's beyond your budget (or by staying offsite you can afford a longer trip!), then I think that you are wise to look at other alternatives. HTH.