If you don't feel it's worth the money, don't renew. If, on the otherhand, you use all the various features and feel you get a lot of use from the service, renew.
I never used it when I had it. That's a nice little chunk of money. (Think computer accessories ) The only 2 things I liked was the online address book and checking my e-mail from anywhere, but I since found out my ISP provides that too. I once heard an argument from a fellow .Mac user that without .Mac you cant access your e-mail when you are away from your machine. Yes, you can, with almost every ISP. Those 2 things were all I needed it for, but if I can do it for free why pay $100 a year? Some people use the features, I don't. It sounds to me like you don't really use it enough to justify paying that price.
I never thought .Mac was worth what they are charging. The address book syncing can be accomplished easily enough by digging into preferences and copying across multiple computers. Not as elegant, but how many times in a day do you sync? Same with Safari bookmarking.
My ISP emails travel with me by way of POP so .mac mail again is useless. Don't get me started on Backup. I have a 250GB HD and Silverkeeper to handle that task.