Both of the different kinds have advantages. The SE's seem to encounter more problems, with the steering mostly. The regular ones are very easy to tri-cell whereas adding more power to the SE's doesn't work because they have a voltage regulator.

I have both and like both. As for the upgrade kits, good luck finding one. I can't believe your RS had one recently. You can look on ebay and find different motors sometimes. I stocked up as soon as all that stuff went half off and I'm glad I did.