not much, most collector off-hands are +30 always and have a 20% recharge or +1 skill mod.
ive never seen a Air Magic collector off-hand item, but i would assume there is one.
Cowsn, that information is wrong. Most collector items offer energy +12, 20%/20% faster casting/recharging. The ones with the 30 extra health usually come with -1 energy regeneration and do not provide any casting/recharging benefits.
All that aside, the 29 extra health may be of some value to an air elementarist, but I would typically expect casters to be more interested in the 20%/20% benefit of the collector storm artifact.