Chess Mentor, and now also the video lessons, are excellent if you want to improve. You can find quite a few lessons on the internet at various sites, but I have not come across anything that rivals CM for quality, that is any cheaper than diamond membership.
For things like tournaments I don't think it is worth the money - just join more teams for their team matches, and accept more open seeks. Spending money just to play more games is wasteful in my opinion. Investing in improving your game is better value, so for me the decision would depend on what you want to gain from the site.
Chess videos, chess mentor, tactics trainer, offers of marriage...wow, all for pennies a day!!