Well, I can understand and appreciate all the personal preferences here... I have a boatload of them myself.
Fact is though, I have a couple of PC-based processors running on mountaintops right now... one on a new (then), off-the-shelf Dell computer. The other is running on a similar Dell I got off of Ebay, just to see what kind of fun that might add to the mix. Both have been in service for over 2 years with nary a blip. Neither BBP nor Stereo Tool has "crashed", nor has the XP operating system... not once. The equipment is proving itself in daily, full-charge, "mission critical", unattended use, so if the client might be well served by a little "out-of-the-box" thinking, then I have no problem setting personal biases aside long enough to try something different.
I get a level of performance from these systems that I can't duplicate for the money with hardware boxes. As for reliability, I HAVE had "blips" from other broadcast equipment, built by companies that are well respected here. You fix it and move on.
I don't lose sleep over the processing, custom-built or not. For that matter, I don't lose sleep over any of it. If equipment only failed once in 25 years, many of us would be looking for new careers, and a lot of engineers wouldn't be very familiar with the technology we maintain..
As for keeping "legacy" gear running: I recently sent off an old AM Optimod for reconditioning by Bill and Kim Sacks. There wasn't any debate about the issue... the client wanted to keep the box. It came back, sounding great. It'll be interesting to keep an eye on, but so-far, I haven't had to touch it since I put it back in.