Actually bear the rote in question wasn't about you...
My bad! I actually didn't realize it was you. I didn't think you were talking about my character. I've been awake going on 40 hours now so I'm getting kind of goofy.
I have been working on a big Area-of-Effect spell for use against the shambling hordes of minions and whatnot. here's the base version of the spell;
Death from Above – Strength 6 (Air/Fire, Lightning); Requires Gauntlets (Focus Item)
Effect: Launches a Strength 4 Attack against every chosen target in the same Zone.
The first stage of this spell is a Maneuver that set the Aspect “Target-Locked” on the targets. The markers initially appear as red laser beams that hit the ground then chase down the targets until they can get a lock. In the second phase each target being struck by a bolt of pure electrical energy.
Basically thematics-wise it's supposed to mimic an Orbital strike, or multiple Strikes (The character in question is a Combat Warden) and I wanted to have a version that he could use that was just ridiculously overpowered for those...special occasions. Not intended for daily use, just for when the fit really hits the shan.
Hrmm...is it possible to effectively add a Catch to a spell like "Only works in open-air areas"?
As for the type of spell you are describing, catches could be house ruled but they are not RAW.
As for an area attack, it costs 2 extra shifts of power(which you know) to attack everything in one zone. One cannot pick and choose targets. It costs an addition 2 shifts for every other zone than one. The raw is pretty clear that attacks of this nature will damage friendlies too.
Taking that route would require 6 shifts of power for a 4 shift attack to /everything/ in one zone.
What you're describing both thematically and mechanically (choosing multiple targets) is actually splitting the spell. This is done using the "spray" rules in the book, but for evocation.
Basically, after you declare your shifts of power and attack (I suppose it could be done with a rote too - still works the same) you then divide your power and your attack roll however you choose except there must be at least 1 to each value.
In other words, selectively targeting multiple enemies is very difficult to do and with diminishing returns.
If you really want to nuke an area, a zone spell is probably best but you can cause friendly fire that way. I'm assuming that Evil Hat did made these rules to further make wizards think twice before calling down the fires of heaven and such.
Once again, sorry for the mixup. Once I realized what I did I had to come back and give a more thorough answer.
As for the rote question, if your discipline is lower than 7, making a six shift spell into a rote is probably definitely a good idea.
Since I am in the game in question, consider this. If your character has a blanket AOE spell, you can still nuke. You just need someone with a high enough defense, enough fate chips, or a strong enough shield to lure all the baddies in one zone away from everyone else. Then you nuke like crazy.