I did this recently, for an early morning EWR to SFO ps service. Against my principles, but if I could upgrade every flight all year to a bed for $299 I wouldn't need status, and it's less clear to me each day what status is actually good for. This was half the fare difference to buy P class in the first place (with all benefits); my more recent offers have been closer to the entire difference.

I read the rules very carefully, as this was an experiment. The $299 was a nonrefundable fee, not transferable on a voluntary change of flight. It did earn double PQMs, but no PQDs (I just earned $97 for the paltry base fare).

United is pretty stingy on anything they call a fee. Paying for Premier Access (e.g. for no status family members traveling with instruments) is a similar minefield.