Following your solid reasoning I've given up on the idea of replacing a perfectly good SSD disk with one exactly the same just because it might - at some point - break. As you pointed out - it's crazy to replace a perfectly good piece of kit.
Instead I took the advice given and have bought a spare hard drive of the same make, type and size and it's now sitting on my shelf in its box, unopened. Should the current SSD ever die, I can swap them over with minimum downtime.
To perform this swap over I took another piece of advice given and bought a decent backup tool. Until recently I'd been using Windows Backup & Restore to do a selective backup. But I have never done an actual restore from a Windows backup and have never felt particularly confident that it is bound to work.
Now I've spent some money and am using Acronis True Image 2012 to do a complete daily backup of the whole disk to my NAS. I now have almost complete peace of mind. The laptop blue-screened last night which was a lot less scary an occurrence than it used to be.
It goes without saying that a backup is of little use unless you know it works. My next job is going to be a trial run. I'll stick the new SSD in and try to restore from the Acronis backup. Assuming it works I'll re-format the new SSD and put it back in its box before returning to the old SSD. I can then find something else to worry about.
What Else To Worry About?
My two main fears are loss of data and loss of internet connectivity. I've just about got data covered and also now think I've got the connectivity covered too. A couple of weeks back I woke up on Monday morning to find there was no internet connection. When I went to reboot the router I noticed there were no lights on it at all.
Despite it being under guarantee I couldn't wait to get it fixed so I quickly ordered another of the same router on next day pre-9am delivery. When it arrived the first thing I did was try the new plug with the existing router and, lo and behold, it worked. Now I could have been a bit naughty and sent the new router back for a refund with the broken plug, but instead I've kept it and had Draytek send me a new plug. I now have a spare router and all the config settings for it backed-up.
The only thing I don't have covered is loss of connectivity due to any issue with my ISP. Although, they are really, really reliable and I have no real cause for concern. I pay over the odds for a "business connection" and it's yet to fail.
That said, I've been thinking of re-connecting the 2nd BT line in to our house and using it as a broadband-only line connected to a cheap ISP. The router can then failover to it if needs be. That seems like taking it a little bit too far though...