Hmmm, all eTrex Firmware versions I've seen have two digits after the decimal point, so you got 3.70? When did you purchase your unit?
However, my Legend is about as old as the original posters. I have done several Firmware updates and never had any trouble other than when going from 2.5x to 3.something I lost all the custom settings (as promised in the release notes).
The updates are IMHO worth the trouble. I forgot which version actually fixed my Legends map upload problems (threw comm-errors in full speed) or when they added that nifty battery type selector so that fresh charged NiMH's don't show up half-empty (or is that half-full?).
Just make sure that you have a fresh set of batteries in the unit. An interrupted Firmware upload can seriously confuse it.
Also, if you have MetroGuide, get that update as well. They finally fixed this annoying "route hides highway numbers" feature.
Jan