It seems that when your code is shonky (and you have an inkling that it might be), valgrind is where to look. It’ll point to things, even when your program appears to be working, and say “err, are you sure that’s right? it looks like you’re being a bit of a muppet there”. And you can ignore it (I did, mostly cos it took me a while to figure out what its error messages meant), but eventually they’ll come up and bite you in the seg fault.
In short, I feel it is going to be invaluable. Even more so than it has been tonight.