Sinclair,
Thank you for all of this information and your real life experiences with these systems. Since I do not have large dollars invested in a control system as of yet, I have the luxury of trying things out slowly. Please correct me if my interpretation of your write up is off in anyway. My personal take away from this is to set up DCC on a track with a converted old conventional engine that I have modified to DCC operation. Once that is fully functional and if there aren't insurmountable hurdles, purchase a Lionel Legacy control and put both on the track and check out how they operate or not. Of course paying attention to electrocoiuplers. My thinking would be as follows: if this works I can run the MTH loco's switched to DCC (not sure how many have both capabilities DCC & DCS) And all Lionel Legacy loco's and my old converted conventional loco's.
If this fails then my route would be to use ERR conversions on old conventional loco's, Hook up the Legacy system and purchase a DCS system. Before your input I was tending to go the Legacy/DCS route (which I think was over 1k in costs) So I would wind up there in the long run. Does this sound somewhat logical or totally nuts! 
Thanks
John
