Well....
Sonar is much more of a resource hog and it's still a bit buggy, but...
I opened up CW PA9 the other day (which I have looked at since April) and it seemed so, well, anchient.
The interface is night and day from PA9 and if you do anything with midi, the DXi Synths are very nice, as are the automated effects.
I paid $99 for the upgrade and haven't regretted it a bit, but I can't really say I'm doing much more with Sonar that I couldn't have done with PA9. I enjoy working on it more, though.
Hard to give you a yes or no on this. Bottom line is how precious is the $150 to you and what else could you do with it. I find some of the features great, and I couldn't go back to PA9. But waiting for version 2.0 is an alternative (except you'll probably pay more).
I realize this was a pretty wishy-washy response - but it's really a call you'll have to make for yourself. PA9 is a fine program, and certainly acceptable for recording. Visually Sonar is light years ahead of PA9, and to me it's easier to work on. But if the bottom line is getting good sounding audio recorded, there's not a lot of difference. In other words, it ain't gonna make you sound any better.