My moral compass must be slightly bent compared to some of yous guys then.
I've always been of the opinion that it ain't a crime until you get caught.
So with that in mind, my answer would be thusly:
If the land is owned by people who are a. The council, b. Serial clampers, I would pay up.
If it's private land and you're just gonna get a ticket on your windscreen/in the post from some private body, I would laugh, loudly, as I throw the legally unenforceable ticket in the bin and get on with my life.
Pay or not, people who try to charge you for parking on a Sunday are going to hell anyway.
edit: the reason why I would do what I would do is because I have made a reasoned choice based on what I believe I can get away with.

