New Owner needs advice on maintaining value versus remodel/update

I just bought a 74 Argosy 24. Although inside it is almost perfect, the outside paint has some scratches on the top, I am not too fond of the green countertops or the dated interior. It is white on the outside and I was thinking about painting it or stripping it. I also want to update the interior but am hesitant because I don't want to decrease the value. It came with everything from the dealership including manuals, Bill of sale, etc. I don't know what the value currently is but when I pulled the dirty thing into my driveway last night, my neighbor offered me three times what I paid for it, as it set. I just finished washing it and cleaning it up and it is night and day difference. My question is, should I update with granite, hardwood floors, New cabinets, or would that decrease the value? I know they are hard to find in their original state but let's face it, the 70's, although cool, were not known for great decorating style...lol