You've got a point. However, I get the feeling that the spell might feel a bit cluttery with 3 different settings, mana cost, etc.
The increase in magicka from Touch to Target range is a constant multiplier, however. And Self and Touch are the same cost, as far as I know. So the spell could simply show the normal cost for Touch range, and if the player really wants to micromanage that much, he can just calculate the increase himself.
I recently made a mod for myself that did exactly this in Oblivion. However, it doesn't work so well with Oblivion's system, but I'm sure it would work perfectly in Skyrim, thanks to dual-wielding.
My idea was to use the Block button for switching to Target range, which works pretty well. You could even implement a zooming perk, like the one for Marksman in Oblivion. Only the Self range thing is problematic, because it does slow you down a bit if tapping/holding needs to be checked everytime. Wouldn't be a problem if the game could figure this out while it was already playing its casting animation, but then they'd all have to start with the same animation and then abruptly change to the Self/Touch/Target animation.
Actually a spell could have a default range, but you could change it to one of the others by pressing a special control. Or maybe two buttons, one for Self and one for switching between Touch/Target, just to be on the safe side. V and B would be perfect if C is still for casting, for example.
Then we could have the best of both worlds - only one spell for all ranges, and holding down the casting button could increase the charge.