As another Happy KISS owner I have to say that as you have the second most numerous recreational unit on the market with one of the best scrubbers you are in a pretty damn good place to start.
I too have looked at the rEvo and it does seem to have been designed with similar intelligence, I would be sorely tempted if I was buying now, particularly as they've got together with Shearwater who IMVHO make cracking kit.
If you did change your mind I'd wager someone will tear your arm off for the Classic KISS, they are in constant demand, you'll probably get what you paid.
Lastly, ask your instructors about the KISS training and what it would take to cross over to the rEvo if you did later change your mind, from my examination of the unit I would have thought the cross-over would have been a joy ride for both you and them!
You have the enviable position of owning the best rebreather on the market and to be considering the only rival
