I ended up using 3M General Purpose Spray Adhesive to attach the thin plastic parking lot material for the motel/ restaurant and for the Mel's Drive in. It took a few attempts to get the flexible and sticky parking lot pieces in the exact correct locations. Each time I had to yank it back off the wood base to reposition it, I thought I would ruin it, but it, but eventually I got it all down in place. Once that was down, I could use the construction adhesive to attach the rest of the Walthers sidewalks and curbs. Between the Motel and the Mel's Drive in, I used the Walthers curbs without the sidewalks.
Other than the trees that will be around the Motor Hotel property, there really isn't much vegetation on this diorama. But there is a grassy area between the motor hotel and drive in, and there's an actual lawn in front of the restaurant building. I took some pieces of 1/8" thick styrofoam sheets, and cut them to shape, to match the height of the Walthers sidewalks and curbs in those areas. I painted the styrofoam flat brown, then sprayed each piece with spray adhesive and sprinkled Woodland Scenics turf on them to represent grass. In some areas, I sprayed more adhesive and again sprinkled on more grass to cover some bare spots. When the grass was dry on the styrofoam pieces, I turned them over and sprayed more adhesive on the bottom of each piece. Then fit the lawns into place like pieces of a jigsaw puzzle. I won't be gluing down the buildings, but I did spray adhesive on the bottom of the Smalltown USA sidewalks that make up the pool surround, and put those pieces in place. That will actually help to keep the motor hotel in place so it doesn't slide or get bumped out of place too easily.
Next step will be the tedius project of making alot of parking spaces.