How I usually go about stuff that you mentioned:
1. a combination of good fort saves and rerolls.
How to get good saves:
a)plain save buffs like Greater/Superior Resistance (SpC), DMM Persist Mass Conviction (also SpC, if you have a cleric that's into that), extended Benediction (Complete Champion, also if you have a cleric/paladin on hand, also grants a reroll)
b)get a good Con score. Most good shapes you can Polymorph into have a good Con score.
How to get rerolls: Alter Fortune (PHB II), Mantle of Second Chances (item from MIC), Lock Blade (item from DMG), see benediction above).
It's not hard to make a wizard that never fails a save
2. most blasting has saves(usually ref half, turns into ref none with a Ring of Evasion) or some form of attack (usually ranged touch attack). It's not hard to get both defenses high enough to be safe. See above for saves, and a good Polymorph+scintillating scales does wonders for touch AC.