There are indeed 2 valid points in this discussion. One, whether or not our car computers are actually like or similar to our PC's & Two, will our car computers fail in the long run.
SRT Six answers the first point & he's absolutely correct with the reliability of the actual electronics. In 30+ years of working on computers (PC's to mainframes) I think I've replaced maybe 10 or so actual CPU's & related processors. Memory cards & chips, power supplies, cables & connectors - enough to fill a landfill but the actual electronic brains? Nope.
Now will the whole shebang fail in the future? Probably. It's not the electronics; it's the stuff that keeps it connected. Cold or cracked solder joints, oxidized connectors, loose boards, heat, split cables, rodents, nuclear war, Rosie O'Donnell (OK, I'm only semi-kidding about the last 3!) all those will be the killers & just try staring at the back of a circuit board sometime trying to find a cracked or crappy solder joint. Such fun shouldn't be legal.
It might not be a bad idea to slowly build up a wee collection of some of the more vital electronic components. Forget the switches & little things; odds are that in the future you'll be able to score those from junk dealers. Keep them in anti-static bags (available from Radio Shack or you can ask your IT guy at work) & keep them in a cool, dry place. Voila'!