I haven't seen Ozone 2 yet, but Ozone 1 is basically an all-in-one mastering plug-in that includes EQ, Reverb, a stereo-imager, a loudness maximizer, a harmonic exiciter, etc. You already have equivalents to most of these as invidual plug-ins included with Wavelab.
Like many things, however, you may find that you "prefer" some of the Ozone stuff to the equivalents included within Wavelab, and vice-versa. Some of them might sound better to your ears, or you might prefer the visual aspects of one over the other (Ozone does have some nice visual features, such as the spectrum analyzer built into their EQ).
I guess you could compare this somewhat to a painter's pallette. If you can afford it, the more the better. For ex., you might already have "yellow" in your pallette, but you might not hqave the exact shade that you want. In other words, Ozone's reverb may be just what you are looking for in one song, while Wavelab's could be the right one for another song or style.
Personally, if I already owned Wavelab, I wouldn't invest in Ozone. But like most things, it's a cost-benefit decision you need to make for yourself. Bottom line, though, you won't be getting much in the way of "new" tools with Ozone. Just different spins on some stuff you already have.
Do, though, download and read their (free) guide. It is a pretty good primer on mastering.
The presets aren't bad at all. The excitement is definitely there 
I will look into it more...