Well, combining everything together, you can now get to the stage where you succeed on saves on a 3+.
First aid (+2) human feat (+1), the new human feat (+2) and the background that gives you +2 to saves when you're more than 5 squares from allies, for a total of +7.
I don't like that the feat which makes hand crossbows the best ranged weapon in the entire game for a rogue (possibly excluding the dagger) is drow only. It's probably slightly too powerful for a single feat at all (although that might be dependant on if there are any rogue-useable superior crossbows: if so, this should be even in power to those).
When somebody asks you to convert damage to cold for 'fluff' reasons, agree to it as long as he will never take Lasting Frost. I bet that in 95% of the cases interest will wane, exposing the munchkin behind the fluff.
This is true for paragon tier, but not at epic (for holy damage at least). Holy damage actually has the superior feat at epic tier (as opposed to, say, fire).
Personally I think the real solution should be to implement elemental damage feats that are actually good and share some synergy, so that choosing wintertouched is actually a hard choice. I mean, was it not obvious that fire and acid should have feats that grant ongoing damage (say 2/5/9 at heroic/paragon/epic? I think lightning is good except for how rare crits are for a wizard (and the fact that you throw your crit away to gain the feat benefit: take that away for starters) and thunder is nice too (blast 4 thunderwave? Yes please).
The problem is that wintertouched/lasting frost are too good compared with the available alternatives.
You could also drop lasting frost down to 2 vulnerability and wintertouched to a +1 bonus to hit instead of granting CA.