Ok, so I just picked up a Raleigh Rapide mixte for $10 off of craigslist (passed up another $10 ten speed too, but it was an old JC Penneys bike, no lugs, figured it wasn't worth the effort).

I figured even for a low-end bike, $10 is a pretty safe investment on my first flip. I figure I could probably put this back on craigslist in a month (when freshmen start showing up for college) with a pretty basket on the front for $100-150 and sell it no problem with zero work on my part, except.

So here's the question—how much work do you put into your "flip" bikes?
Or rather, where do you find the sweet spot for money spent vs. value added?

To give an idea of where I'm starting from, the Raleigh Rapide is clearly a lower-end roadbike—cottered cranks, suicide brake levers, stem shifters, dork disk and a chainguard bolted to the chainwheel. I'm guessing its from the early 80s (judging on decals). That said, pretty decent condition—not a lot of scratches, no dings I have seen, and rust is fairly minimal. Most significant rust is on the headset, and there's a little oxidation starting on the cranks. Should clean up nice enough though, definitely one of those bikes that can look really great from a distance of a few feet.
The one here is nearly identical, except that mine is a mixte and not in NOS condition.
Tires were flat, but tubes seemed to hold air when I got it home. Tires do have some cracking. Wheels are fairly true. Brakes will stop the bike, although the pads are not so rubbery, and they aren't adjusted very well (both seem to want to hang to one side, rubbing the rim even though the wheels are true—how is this fixed?). Shifts into all ten gears (not the smoothest, but probably not much worse than it was new, really).

So what to do? If I find that the tubes are holding air well, then this bike is rideable right now. Should I leave it be and let the next owner deal with new tires, brake pads, etc? Or do you find that it's better to get the bike as close to "new" as possible?