Skipping rage skills?

[bugmenot]

I'm quite enjoying Lina Ice Ball (rolling ball thing), but so far I've chosen not to upgrade it.

Completely un-upgraded it costs 10 rage, if I upgrade it the cost goes to either 15 or 20 (can't remember), but the damage / hit points only goes up slightly (about 10%?).

Even at level 1 the Ice Ball seems pretty hard for the oppositon to kill.

In a normal battle I can get 10 rage on turn 1 (phoenix, inquisitors + a few ranged units).

Has anyone upgraded the ball a few times, does it become an essential killing machine, or just a too expensive gimmic than you never use?
________
starcraft 2 replay