To be honest with you, I'd be looking at upgrading to 4WD - I think it'll suit this style of machine a lot more, and no matter what you lift if you position the wheels right you'll always have your weight over at least some of your drive. Likewise there are other options for wheels like Banebots but they are a little expensive. Very good for grip though.

As for not righting on its side, perhaps you could add some side spikes to stop it getting stuck there? If you upgrade your batteries or replace heavier materials for lighter ones where possible, you could easily have a Razer style tension cord wing thing (which would be absolutely awesome if you were to do it) or you could make adjustments to your body shell to help it roll over on its own...