Can't say that I have any experience with a 4cl Solara, nor the older V6s for that matter, but depending on what mods are done and how you drive/where you drive will make all the difference.
All I can say is that I live in the mountains and drive like a maniac most of the time with my heavily modified V6 Convertible (Auto & heavier than the coupe) and I still manage to average between 22-25mpg. If I cruise down to LA I usually average about 27mpg on the open hwy.
Hope that helps some. I know others have had better mileage with stock setup and take it easy on the gas.
Jeff