I moved over from WM5 in December having been a WM5 user for many years. I have the Blackberry Curve 8320 unlocked from T-Mobile with a Blackberry Data plan. I can't imagine life without my Curve - it does what it says on the box, so to speak. My opinion is this - if you want email on demand (push) and want to benefit from the Blackberry experience as it was intended you need to get a BB data plan. There's just no way around it - the experience with a gdp is like night and day. You can't do much without it.
The generic data plan is cheaper but I kept mine only a few hours before I changed it to a BB data plan. If you're with anyone other than Rogers, you really shouldn't be complaining about the cost of the BB Data plan at all.
Don't expect the same on-screen experience of the screen with WM5 - it's different. With some of the Today themes for the BB you can have your Today items on-screen. Experiment with a few. I've purchased some great themes for my Curve and very nice applications and I am very happy - I don't miss SPB apps or even the WM today screen.