Heh, 25 by the Ice Cave is (wayyy) overkill. Only need to be 17-19 Plus, it really wouldn't protect you much against the main dangers in the cave: COCKTRICEs, SORCERORs, MAGEs, FROST Ds(when treasure collecting) and the EYE.
WarMECH wasn't all that bad, honestly. By that point in the game, you'd ideally have someone over 400HP - thus, NUCLEAR (NUKE) would keep at least one guy alive. Hopefully, you can run. Combine that with the fact that it's hard to run into him without going up and down the bridge at least twice, you'll usually won't have to worry about him.
FF1 is hard. Even if you've played the game a thousand times before, RedGOYLEs will wipe out your party at least once during Gurgu, TRANCE will still drive you absolutely insane... etc. My point is, it's hard looking at the sequels of the series. All they've done is make it easier (and more time consuming, but that's beside the point)
Edit: WALL does not effect the power of NUCLEAR or NUKE. NUKE is a non-elemental spell and WALL does not reduce this damage. There is no way to lower the power of NUKE. You're better off casting FADE/NUKE/FAST.
Edit 2: NUKE/NUCLEAR deals between 100-400 points of non-elemental damage. Period.