I have a G1 (had it since day 1), and I also wont be able to get another phone which does not have a hardware QWERTY keyboard. I've had pretty much every MLIGN ROM on my phone, and the last one is by far the fastest, so it will be worth taking the time to flash it.
One thing to keep in mind with Android and not having a data plan is that it automatically sync's your contacts and backs them up on google's servers, as well as your app download history, and if you have a hero it also syncs your contacts with facebook giving you their bday info, pictures, comments etc. Of course those things can be disabled, but its one of the reason why I like android so much. Using GPS also requires data, quite a lot too because it has to download the maps.