I only have two tmcc type engines and one dcs. I have never ran them. They came in collections with other stuff. The idea of having an engine with the modern day features does intrigue me. Seeing them operate at shows and club runs is awesome. However, I am unsure how I would react to some of the electronic problems listed in these forums. Probably like a two year old beating the floor with my fists.
I've looked at some of the basic electronic e-units and they look fairly repairable. Once you get custom chips on the board, its a big problem. Electronics manufacturers will often buy up all end of life chip inventory to guarantee future supply. I'm not sure how the big three train mfrs approach that issue. Their chips are usually copyrighted, so the third party would need a license to make replacement boards.
As long as the motors are good, you should be able to salvage the engine with an after market Elec e-unit. However, I would be upset loosing all the other features.
I think i would approach the high end engine purchase like any other electronic item, looking at failure rates and customer service/repair centers.
P.S. all of my old Lionel postwar and mpc still work flawless and I repair them when they break. (I didn't need to mention that, did I)