Welcome to BF and back to cycling! On your bike... If it works OK as is--hop on it, pedal away and don't even look back. If it needs a little $$ I might go for it, but... I'd have a good LBS look at the bike and recommend just how much $$ it'll make sense to sink into it. A WalMart Schwinn may (?) or may not be worth putting a lot of $$ into. You need to take a dispassionate look at the value and potential value of the bike and make an informed and prudent decision there. Good luck with it, though--and as I said, if it works OK as is then get on it and ride it into the ground.
You may find good insights and suggestions on the rebuilding quandary in the Bicycle Mechanics forum...