"Most QRP work is at frequencies less than 30MHz. While 6m might work, tropospheric ducting, sporadic E, etc are touchy enough that adding in QRP operation wouldn't be pleasant."
Not my experience at all. I have been wallpapering my radio room with 1st place wins as a QRP entrant in the ARRL 10M contest in December for a couple years.
During a Es opening my 5 watts might only be S9+10dB whereas a guy with a 1500 watt linear would be S9+30dB so you can see why its not much of an issue.
Before I got a modest brick for 6M it was the same deal every July and December. I'd have 5 watts out and work guys 1000 miles away who had signals S9+20dB and I'm sure I was "merely" S9 or so on their side.
Another thing is the ops on 6M are gentlemen, by self selection this is not 80M or 20M sideband. They're glad to work a "weak" signal and don't turn down their RF gain or whatever those HF ops do.
When propagation smiles on you, power out doesn't matter. When it doesn't, well you're screwed even if you have illegal levels of power.
I live in a part of the country where the 1000 mile Es donut covers pretty much all the sand states. So I have a lot of Grids! I near got DXCC during just one VHF contest in the spring in just one day!