My comments on the topic come in two forms: thematic & game-balance.
Thematically, self-inflicted damage (spending a consequence to power a spell, or taking backlash) is a sacrifice. If you can absorb that with toughness, or instantly heal it with recovery... that's not much of a sacrifice anymore, now was it?
In terms of game balance, spellcasters are already one of the strongest things out there; letting them fuel their powers off of recovery, or use toughness to absorb backlash, just makes them that much scarier - and they really don't need it.*
Also - bumping your elbow? For someone with toughness, they wouldn't even notice. To some extent, injuries (read: the names assigned to various consequences) need to be scaled to the target; I still remember my players' first encounter with ghouls. "Ok; you got a solid hit in; the ghoul will take a minor consequence of 'bullet hole in the leg'" "That's a minor consequence?!?" "It is if you're a ghoul."
*Footnote: the exception to this is if other players are just utter cheeseweasels, and the GM decides to let them get away with it. For example, I've seen a player decide that it's clearly fair play to try to stack literally everything that could give a bonus to melee attack rolls - vampiric powers, plus the sword of the cross' special purpose power ("re-flavored" & purchased on its own, of course, to avoid its original thematic limits), and mortal stunts, and so on and so forth. Oh, and then paying for all that with, among other things, a meaningless feeding dependency that applies to a small enough subset of powers that its odds of having any game-mechanical effect are less than one in a thousand...
But if you've got people doing that, one custom power is really the least of your problems.
