I can see why your are reluctant to purchase another C4s, once bitten and all that...
You had a very bad experience and it would put anyone off repeating it especially if the same thing happened again.
Having said that I have had a few BMW M cars and while they are really nice fast cars and sound great when revved to the limit. They do not have the same driver experience that a 911 has. Once the initial honeymoon period wears off I think you may feel a bit underwhelmed and that itch for a 911 will still remain.
I bought my latest car 18 months ago and knew that I would have to spend some cash on it to get it up to standard. I also knew about the pit falls of IMS,RMS and bore scoring. But for me it had to be another 911 and I will drive it and enjoy it.
Ok there is always the possibility that it may suffer from bore scoring and at 73K miles it could be imminent but I'm not going to worry about it. Not because I have pots of money(which I don't) but because I could walk in front of a bus tomorrow and be brown bread but at least I had the opportunity to drive a car I truely desired that never fails to bring a smile to my face.
Just my tuppence worth.
Good luck with your decision.