I agree with Terpfan. I would try to get another guy out of the deal.
My first thought is that you shouldn't make this trade unless you can get someone else solid in addition to Bennett. Bennett is fairly untested in a usually pass-dominant offense. In addition, since good RB's are so hard to come by and are getting injured all the time, it's important to have a really good secondary and a solid back-up in case one of the top guys goes down. Bettis and Smith are not great backs, but are solid. Remember, too, Smith is trying to break a record this year.
If you think you can get Bennet and ANOTHER decent RB, then I'd make the trade. Otherwise, sit on it. But it all depends on who you already have on the roster.
Who's your #1 RB? What is the rest of your team like?