I'd say in this case you just get the +2 bonus with respect to Bob (essentially Bob has a harder time with the spell/effect than Steve).  So in the 10 person scenario, you'd get a +2 bonus on all of them, rather than just one of them.  That seems to make the most sense.

Mm, the thing is that technically it's only one casting roll and as such you don't really get to "divide" the bonus from multiple tags among different targets on the zone castings, so it feels like the Rules as Written would leverage that +20 bonus, if not the Rules as Intended.  Still, since it's basically a bonus on a to-hit roll it could just as easily be handled per target.  Probably doesn't matter though, as if by some small chance there isn't a rule against re-invoking the same aspect for one roll there really should be.

More interesting here is that Frank is saying you can do a zone-wide maneuver with a spell, which actually isn't something the rules spell out as possible

Good catch!  There are clear rules for multiple targets on Attack rolls, and I guess I always just made the logical assumption that those could be extended for maneuvers.  Didn't realize it hadn't actually been spelled out before, and that really would be crippling for maneuvers.

The appropriate GM response to that sort of request is to roll up a newspaper and smack the offending player on the nose whilst yelling "bad!" in a sharp voice. 

I'm very much inclined to agree!   
Still, I find it an interesting mental exercise.

Thanks for the responses!