SEL precautionary landings: what's your experience?

I have landed because of mechanical failures maybe once every 300
hours. I had a vacuum pump fail (VMC, I'm happy to say), an alternator
(In the clouds but soft IMC), a magnito failure that took out a bank of
spark plugs (probably IFR, I don't remember for sure) -- things like
that. Nothing really awful, but every one caused me to land a couple of
hours short of my destination. Most of these happend in my own M20J
which was (at least I think it was) well maintained.

What about those of you with 500 plus hours: what has your experience
been like? Am I just unlucky, or typical?