BOTTOM LINE:

Is ProTools the best performance you can get for the money?
Probably not.

Will it draw more clients, dollar for dollar, than any other investment?
Yeah, it will.

Audio purists HATE ProTools (or mixing 'in-the-box' in general -- hell, most of 'em hate digital), but businessmen LOVE it.
Also, I agree w/Justin, et al that if you HAVE to start from scratch learning software, it's the easiest one to learn. That being said, I use it only for editing, not tracking or mixing.