I think comp upgrades are fine at the gate and a nice perk that I enjoyed in my FO days (it would be dumb to fly out with J seats empty). On the other hand, if I bought J and have IRROPs, I do not want to be sitting in the back because J is full of comp upgrades that were handed out 5 days in advance. If you want to be sure you sit up front, you should pay for it.

I feel similarly about RUCs and GUCs as GagaPilot.