I've used the CityPass in NYC before and have ordered one through a Canadian reward program, Air Miles, already for an upcoming visit I like the convenience of bypassing lines as well as the relative value they offer. While Sept. will be less crowded than summer, the lines at ESB can still be long so having a CityPass will save you time.

Beyond the actual admission vouchers the booklets also include a few other savings coupons as well like $2 off Guggenheim or 15% off restaurant discounts that you might find you'd also use while sightseeing.

MHO is to go ahead and get one as I find them a useful value.

BTW I finally made it to MoMA last year after missing it in previous visits and plan to return as the outdoor sculpture garden is a wonderful space well worth experiencing on a warm Autumn day.