I have never bought an accessory kit for a toy that I did not already own. I have also been very picky about the ones that I do buy. Example: I own a Classics UM but not the City Commander as I have the TFCon Powered Commander.
I feel that all of this third party craze is a double edged sword. Yes, they are really nice (in some cases) but they drive up the prices to unrealistic levels. This hurts the people at the lower end of the financial scale who might just want the original version. It is a rare fan who is willing to give up an item at cost if they can triple their money or trade up. (if anyone has a close to cost option for the ROTF Bruticus, PM ME!!!) This also results in false inflation of value based on speculative rarity. How many people have been burned by Henkei Rodimus?
Sure we all like feeling that our collections are worth some money but but I feel the real value comes from playing with your friends like when we were kids.