I think it really comes down to two things:
1) Are you watching it with others? Because, I know for me, there's no way in hell I'm shelling out $50 for a 3 hour show by myself. If you can get friends together and get the cost split somehow, then I think it is definitely worth the price because regardless of whether the show bombs or not, you are in the company of others and can have a good time regardless of how the show performs.
2) Can you wait? To me, this is the biggest determination of whether to get a PPV or not. To be honest, I've only gotten three PPVs in the last 12 months. For me, it's economics. If I'm wanting to watch the show by myself, the show has to have a solid lineup and enough build to get me to hit the buttons on my remote. Otherwise, in a month or so, WWE releases their PPV DVDs at a rough cost of about $15 if you get them at Wal-Mart. You could also rent them at your local rental stores just to watch the show at a lower cost. So, for me, it often comes down to this question: Is having the immediate satisfaction of watching the show at $50 worth not waiting a month and get the show at $15? More often than not, I find WWE and TNA PPV's do not fit this criteria for myself personally. But if you have several wrestling friends you want to invite, cut the cost, and have a good time watching the show, I say go for it.