Nonetheless, most bike wheelsets come with a few more spokes in the back than in the front, typically...

I have a front suspension fork and just replaced a back spoke and had the back wheel trued, so that's why I was asking if anyone ever used a mixed set of wheels

A few tourers do this particularly if they've got rear but not front panniers. The rear/front weight bias can get pretty extreme. And they typically don't ride fast enought to smack potholes too badly - not me anyway. For regular commuting I'd just use the same wheels front and back.

Instead of picking and choosing components, concentrate on the quality of construction. Even inexpensive rims, spokes and hubs (not too inexpensive) can make strong wheels if the builder knows what he's doing. After mounting new wheels, check and adjust spoke tension after a couple hundred miles. And once the a rim has gone out of true from an impact, it can be "straightened" through adjusting spoke tension but the resulting wheel will never be as strong as it once was and it will tend to keep needing attention from that point onward.

The dishing of the rear is a factor, too. My rear wheel is much stronger than my front, just like my rear tire is much more expensive and tough than my front tire. It needs to be.