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. The RF upconverter would help with that, however.

Power is easily solved by an external amplifier.

Increased bandwidth would be nice, but 20MHz is plenty. While you might need that for microwave experiments (wifi, gsm, etc, and spread-spectrum experiments), the big advantage of the bandwidth is being able to listen in to everything at once, and see where signals are at a glance, without tuning through frequencies. Being able to glance at an entire band, and immediately see where QSOs are happening is pretty cool. Or you could record all of the FM broadcast spectrum, and decode it at your leisure later. That's not too practical, but is pretty cool. And 20Mhz is wider than every ham band 2m and lower.

And 500 MHz isn't quite enough for voice - SSB is generally 2.3 - 3 kHz. 300-500 Hz is ideal for CW (morse code), and digital modes can use even less.