Like Klaus I get various noises and slight drags from brakes on various cars and they seem insignificant.

If the caliper is really sticking, the wheel will get hotter than the others. If you go out for a highway drive with hopefully minimal brake use, then stop (gently as you can) and feel each wheel you should be able to tell.

In my experience a stuck caliper will make the wheel too hot to touch after as few as several miles. The hot parts may expand and make things worse till everything cools off (like next morning).

I have had calipers which stick only some of the time (on certain days). I don't know why this would be. I just replace 'em if so.

It wouldn't be usual to open up and bleed the hydraulic system when doing pads unless something specific is suspected to be wrong. With ABS systems though the fluid should be replaced each 3 years or so as contaminants or absorbed moisture can cause severe damage.