I can't really afford to hack my phone too much - losing it for a week or two earlier was a real pain. I am hoping to get a tablet though and may well consider that more "expendable" in terms of potential time lost re-flashing.
1.) Always tweak the device by ssh'ing to it, not from fingerterm. Then it does not matter if you break the UI. I use WLAN myself but of course you could ssh in via USB if that's your thing. 2.) Always take backups of the files you modify.