But it seems you are trying to 'balance' a small part of evocation against the rest of the game, when evocation as a whole is already balanced for its cost. This feels like making a powerful ability more powerful simply for the sake of getting free stuff for a character you want.
If you read... well, pretty much every post I've made here, you'll see that's the last thing I want. I'm trying to create a weaker character here, not a stronger one. Instead of throwing around big spells, he uses little spells. Unfortunately the rules make small spells a waste of time, due to the cost of them. A weak focused practioner will have already spent -2 or -4 refresh on a talent without getting the full use out of it, so making him pay more refresh is crippling and redundant considering what he should already be capable of doing. Removing channelling entirely for something like claws limits the character even further and still doesn't really recreate the character concept.
The concept isn't broken, isn't abusing the rules, isn't overpowered at all. It fits right in to the dresden universe (I'm not trying to create a magical plumber that jumps on the heads of his enemies and doubles in size if he eats a mushroom or a man of steel that can leap tall buildings here), the concept of a weak/young/untrained magic user is pretty classic for any universe that has wizards in and there are a whole bunch of abilities they have which will make them slightly more effective in a conflict.
I don't care if it's a +1 or a +2, if it applies to damage only, to the chance to hit only or to some other aspect of the conflict. It doesn't need to be a 'free' ability, precisely the opposite, it should still cost, but it shouldn't cost the same as some reality-breaking evocation. If I wanted to have an all-powerful character I would.
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You're right Tsunami, for some reason I thought that the power of the spell was the power of the attack for a rote as there's no control roll but you're right, the power of the attack equals your discipline and so there are no spare 'shifts' that can be used as spin. I'd say a maneuver would generate extra shifts but with only one free tag, I'd have the same problem as my old ideas. Adding tags on would increase the power level massively again which defeats the entire point.
Your idea to add duration to the evocation spell is pretty much idea number 2 in my original post and still doesn't really work for the same reason. Either it costs lots of energy to go for the 3 or 4 rounds, or it costs little power with the need to top it up mid-combat and only working on alternate rounds. As you said, it can also be abused a little too easily as, I think, can any idea when Weapon:X is variable on the power spent which is why I started down the aspect/manoeuvre route.