In 2007 I was given a Singer "Simple" (3116).
http://www.joann.com/joann/catalog/p...ID=xprd1097744
I have used it off and on over the years to make a limited variety of clothes and quilts. It does alright most of the time, but when quilting (or even doing hems) it jams, even on straight stitches. Even when it was new, it would jam on anything other than straight stitches or zig-zag/satin stitches.
Can be fixed with a tune up, or should I be looking for a new and better machine? If the latter, any suggestions?

Personally, I wouldn't bother having it looked at. Sadly, Singer doesn't make machines like they used to, and this is one of their low-end models. If your budget is tight, I'd recommend looking at a Janome machine, or one of the Sears machines made by Janome. I think Janome give you a lot of bang for the buck. If you are a little braver, finding a vintage machine is a great option, but if you're timid about doing your own maintenance, that may not be a good way to go.

Personally, I wouldn't bother having it "serviced" and replacing it, I sure wouldn't replace it with a new Singer, an old Singer, yes. Go to a dealer and see what they have in your price range, they may have a higher end machine that if new would be out of your price range but used may be in your price range.

Thanks!