Yes, it's what I do as first step clean. take out the electronics and simply wash case parts with dish soap and a scrubbing pad. If heavily soiled I may let it soak in the sink or something for a bit first. Same goes for the keycap, just place them in a tub with some dishsoap and let them sit for a bit, then rinse off... if needed can scrub them also.
Confirm it working properly, if so even in its current state as is dirty I suspect you should be able to get $80-100. It being functional is the important part. If you intend to sell it, it may be wise to just let someone more experienced with restoration take care of it instead of going to more advanced cleaning with thing like retrobrite.