I started on Cubase 3.0 in 1989, and in 1999 went to Cubase VST/24.
Last week I went to Cubase 4, which also came with Cubase SX3.
Personally I don't really fall for the bullshit. For the most part, there was no/hardly any improvement between Cubase VST/24 and Cubase 4. In many ways VST/24 is better than Cubase 4. I think most people would be fine with the free version of Cubase LE I got with a Lexicon Omega 5+ years ago.
I have seen no improvements in Cubase versions unless you want to do stuff that is very, very weird. If you want to do what 99.9% of people want to do then Cubase LE, or any version of Cubase is fine. Cubase LE is a very powerful program. Thinking that Cubase 5 is more powerful than Cubase 4 or SX3 is getting sucked into the bullshit. The power is in the songs, the arrangements and the playing, not Cubase!
The only reason I wanted Cubase 4 is because I need to use Logical Edit, but even when I phone tech support at Cubase most of the people there don't even know what that is.
So my advise is buy any version you can get cheap. I paid $200 off of eBay for a combo of SX3 and Cubase 4. There is virtually no difference between the two programs and I've read the specs on Cubase 5 and it seems like more of the same.
p.s. Cubase 4 still an unorganized mess, with mistakes and goofs left and right, just like Cubase in 1989! I've found at least 35 mistakes in the program and have been talking to the geniuses in Germany about it.