I used to do that. But it's not fun, in hindsight. The term math-fix really means fix. As in, repair something that does not work. Sending them on a quest to get elemental frost and fire for a set of rimefire plate is fine, but doing it every time for every player gets old fast, and they need the armor to stay competetive.
Questing for your stuff is cool, but 4E kind of assumes that players get gear when they need it.
I withheld stuff until they did the work to get the materials for it, and it gimped the party's defensive abilities. That extra 2 AC on the Paladin or Fighter does really matter.
If you want to have them quest for gear, you can try this: Give them a bit of elemental frost or sunleaves or whatever the armor needs. Say what it's for (perhaps a skill check to figure it out -- Arcana/History?). Say that it's worth x amount of gp if spent on the item it is for. Basically, it's a coupon for armor. This sunleaf gives you a 500gp discount on your next set of sunleaf hide.
Then, if they want more sunleaves, you can have them quest for it. If they don't, they can just buy the armor. If they do quest for it, they get it cheaper/free.
Something that just popped into my mind.