Should I buy "green energy" from the utility?

[Hpylori]

I buy my home electricity in Massachusetts, USA, from NStar, a local utility. I've been enrolled in their "NStar Green" program which is supposed to buy 100% wind power generated from sources in New York state and Maine. I've been paying a premium over the usual electric rate for this "green" energy that "supports" wind farms. This is how they describe it:

"By participating in this program, NSTAR customers will support the development of renewable energy resources in the region. Participation will help reduce fossil fuel consumption and greenhouse gas emissions and increase the sustainability of the renewable industry..
NSTAR has signed two, 10-year contracts to supply "green" power to customers. One contract is with PPM Energy to receive 30 megawatts of clean energy from the Maple Ridge Wind Farm in upstate New York. The other contract is with TransCanada Corporation for 30 megawatts from the Kibby Wind Power Project in Maine.
NSTAR is not affiliated with either of these renewable generating companies..."

Recently they've raised the premium for the "green" energy threefold. It now adds 62% to my bill's generation charges.
I wonder if anyone would comment on how worthwhile this program is. Am I reducing greenhouse gas emissions, or am I subsidizing the bills of those not participating in the program? I think by law the utility is required to source a certain % of their energy from renewable sources already.

thanks.