Unfortunately even though Guild basses were all made in the USA back then, like old Peaveys their value is not the same as Fender or Gibson, even though in many ways they are better. In the condition the bass is in, best you could probably get for it, unfortunately, would be about $350.
NJ Guitar and Bass Center has a nearly pristine Guild X-702 in rare turquoise blue sparkle, I think he is asking $799, which means that it will sell somewhere around seven or just under. And again, rare color, pristine condition. With original hard case.
Repainting your bass would not really detract from its value, and may get you more money for it if its well done and in a good color, but you aren't going to increase the value to the $800 level.
Endorsing Artist - Petillo Masterpiece Guitars, J. Backlund Design, Vivid Amps, Fuchs Audio Technology, Bitchstraps