'Yeah, I've heard people tend to get lazy in their old age.'
More like we've just figured out you can check evaporative qualities of oil by simply checking the dipstick................
Great filters become something of a moot point when much of the oil is bypassed around the filter as many engines do.
Guess at flashpoint? When was the last time anyone saw a motor with the oil on fire?.................................I thought so, not much of a guess there if you ask me. On watercooled engines the oil will not flash unless something is wrong, if so you'd see the results in deposits under valve cover. Since mine are clean then I submit there is no need for a guess there. Answer seems pretty clear to me.
Fuel dilution? Easy, there will always be a slight amount, you can't get around it. If more then you will know because the engine is not running right. Modern PCM'ed cars keep that under much, much better control. In fact that is the major reason for engines lasting as long as they do now, the lack of dilution. I can think that out, or no guessing there either.
I use mechanical oil pressure gauges to keep track of bearing condition and the like. You will catch loose bearings before they break stuff if you just pay attention to one. Cheaper than analysis and pay for it once only. No guessing there.
This ain't rocket science, if you keep your eyes open you can detect most of what an analysis will show without getting one.