I voted no, this is why.
WDW Transportation (buses, watercraft and monorails) is available to anyone who has valid admission media.
It is Also available to ALL WDW Resort Guests.
So the only guests that are not allowed WDW Transportation is the guest that does not have admission media or a resort ID. An example is a DTD shopper (non park or resort guest) who now wants to go to, let's say to the Boardwalk. The number of guests that would do something like this will not impact the availability of seats so we are not giong to worry about them.
It IS a perk for resort guests as you have buses come right to your resort to take you to the parks.
With the OP's reasoning, then non resort guests can't use the boats either. Non resort guests can't take the resort monorail to the CR for Chef Mickey's, to the POly for Ohana's ot the the GF for 1900 Park Faire. So how does the day guest get to something like the HDDR? If they can't take the bus or boat, then all they can do is park at FW and walk a mile and a half to Pioneer Hall. Remember, the internal FW shuttles are WDW buses too!
Before I became a driver, As an AP holder, I used WDW transportation from the parks to the resorts for ADR's and such. WDW encourages guests to eat in the resorts, how does one get there? By WDW transportation, of course.
If you limit WDW transportation to "just resort guests" then you are making it difficult to go to your favorite resort for dinner, etc.
Now, why do you pick up guests in bathing suits at DTD? Because the DTD buses go to Typhoon Lagoon which is ...... What...... A WATER PARK.
Checking ID's on a bus won't stop pool hopping. Unless I check VERY closely, I can't tell if you are staying at the YC/BC or the AllStars. All KTTK cards look the same. To check that closely takes way too much time and will be the source of MANY guests complaints about how much time is wasted.
As a driver, I'm not checking ID's, It's not my job. My job is to get you from point A to point B effecently and safely. I don't do it on the cast shuttles either, That's the job for security.