Here is what I use for lapping and scope alignment. This kit is about $33 but it's a one time purchase and it has been a great kit. As for lapping too much, you don't want to lap the inside of your rings to where the entire 100% inside the ring is shiny. The goal is to take the non-concentric high spots down so they don't gouge the scope.
I have a CZ 550 that needed some lapping after noticing that the alignment bars didn't come close. I lapped the rings and about 40% of the inside of the rings needed lapping...This can be seen by 40% of the inside being shiny from the lapping compound.
As for all scope rings needed lapping, I would think all rings could benefit to differing degrees. However, one piece bases like Badger Ordnance and serial # rings like BO rings shouldn't need as much lapping as say Leupold dual dovetail setup. Also, lapping Badger rings voids the warranty so check with the manufacturer if you have some high $$$ rings and don't want to void the warranty.
One last thought, as for dual-dovetail rings, you always want to try and align them first (with alignment tools) before lapping. This will reduce the human error of trying to eye-ball align and then lapping the two axis thereby creating exaggerated non-concentricity.
