One needs to only look at the endless threads of issues with third party roms over at androidforums. I have read them, you have obviously not.
I read them daily. Lots and lots of installation/operator errors. Some roms are not stable and are full of bugs, but you can not "paint them all with the same brush". The vast majority of roms, across many different hardware platforms, are not only as stable as stock, but faster, smoother and have more advanced features.
But this discussion is totally irrelevant, as the type of person that is interested in installing custom roms is the type of person willing to take some risks and put up with having to replace a troublesome rom/kernel/theme. In fact we love tinkering with our phones so much, that having to replace a rom/kernel/theme is just another opportunity to "play" with our phones. Most of the people on this forum are reading the same posts that you and I are reading and are willing to take the risk and endure a little inconvenience now and then. By writing off all custom roms as "not worth it," you are really missing the fun and excitement of pushing these phones to their limit.
It's fine that you don't want to push the envelope with your phone. You are, in fact, in the group that is the vast majority of phone users. Absolutely nothing wrong with that. But it is equally OK to push the limits and install custom roms, kernels, themes, and other hacks.
Good luck with your phone and I hope you enjoy it.