The vast majority of my tube failures have involved the stem and not the outer surface of the tube - I'm open to options on how to patch that, but I've yet to find a good method.
I've also replaced tubes when they are "well perforated" by lots of sharp desert plants. A tire full of goatheads leaves a ton of micro-holes that all leak.
If the stem is shot, yeah . . . you're SOL. If this is the norm for you something is wrong though. Are you properly seating the tube in the rim before inflating? Particularly with Schrader valves it's possible to twist the stem so that it's at a funny angle and is putting a lot of pressure on the rubber near the valve which would cause this problem. Might also be worth checking the valve hole in your rims for any tiny bits of aluminum that could be causing punctures (a little sandpaper should smooth that out).
If there are dozens of holes in your tire, I'd probably get a new tube too . . . but would also replace my tire because there's nothing to stop that new tube from being chewed up in exactly the same way otherwise. The tire (and to some extent tire liners) is the only thing between you and punctures.
$5 ($12 if I'm lazy and go to the bike shop) to 1) avoid the work of patching the tube; 2) avoid the work of having to diagnose the cause of the failure (which may be stem-related or snakebite rather than puncture related); and 3) dramatically reduce the chance that I'll have to change a tire again in the next six months (possibly by the side of the road, in the rain/snow/heat, while wearing a dress)? WELL WORTH IT!
Besides demonstrating some pretty tremendous laziness (swapping a tube is what, 10 minutes if you're having a beer at the same time?), you're assuming that a new tube prevents flats somehow. Why would this be the case?
Even a correctly-patched tube is just not as strong as a new tube; all tubes wear out eventually, and a tube that has already been patched is unlikely to last as long tube that has not been patched.
Why do you think this? A correctly patched tube should last for thousands of kilometers. Provided you keep your tires set to the proper pressure, punctures are usually caused when something penetrates your tire. It doesn't matter how new a tube is . . . it's going to flat out when that happens.
For those less lazy than me, how do you keep the glue in your patch kit from drying up in between patches? Given that I only get a flat once or twice a year, I find I need a new tube of glue every time.
Have you tried putting the lid back on tightly? :P My patch kit is four years old now and the glue still works fine.
