I was fooling around with an AP build on Corki in Dominion one game, and I had the 3% mastery for spell vamp plus a revolver. I was attacking an Urgot in a duel using all my skills including Missile Barrage but I didn't notice my life going back up at all not even a little bit.

I think it would actually be more fun and viable if his AP ratios were brought up ever so slightly too though.

Spell vamp only gets 1/3 of your total value on multi-target abilities, so pretty much everything Corki has would have only given you 1% spell vamp, which would be even less healing than your passive regeneration.