This is the drawback and, in my opinion, a pretty large balancing factor -- stuck in a 5x5 room is just about the last place I want my wizard to be. Especially when it's filled with terrain that limits my manuverability.
I used this method to explain this to my players:
- You can use Healing Word twice per encounter.
- You can use Healing Word once per day.
Both statements are true, and you can't violate either statement.
There is one other reason I can see for splashing some ranger into rogue to pick some TWF powers -- more chances to crit. Combine with that paragon path that allows you to crit with daggers on 18-20, and some Vicious daggers.
There are no feats that increase your chance to hit (with weapons, at least -- and the only non-weapon feat I saw was a Tiefling racial feat that gave a +1 with fire and fear powers). Weapon Focus, Dwarven Weapon Training, etc... only give bonuses to damage.