Others made good points, not the least of which is pictures are needed.

I see nothing wrong with building/riding it as is, so long as the condition is stable. You certainly don't want rust progression to eat away at anything that nice. Other than that, it's really personal preference. If you're the kind of person who enjoys signs of age and use in an object, just enjoy it the way it is. If you're one who needs everything perfect and shiny, you probably won't be happy without a rehab.

If I was lucky enough to be in your shoes, I'd probably clean and wax it, treat with framesaver, and ride it for a season or two, then decide.