I did precisely what you are considering. My first round of applications was not very successful. One acceptance off the waitlist at a school ranked 25+. I accepted the place because being somewhere was better than being nowhere. I retook the GRE over the summer before I started grad school, reapplied in the fall, and now am at a top 10.
You need to think about what is best for you in the long term, given your academic goals. The market is tough. I knew if I stayed at my original program, I was going to struggle to get a job. Even now, being at a top 10, the market is still going to be tough, but I'm in a better position. I'm getting much better training and my interests are a better fit.
I wouldn't worry too much about betraying any future advisor by leaving. First, it's not uncommon for a student or two to leave the program, for whatever reason, after one year. Second, most faculty are not going to invest heavily in a first year student...it's not like the sciences where you are working in their lab for them. In fact, when I told my assigned advisor at my old program that I had been accepted to a top ten and would be leaving he was super supportive. (I hadn't told him about my applications until I got the acceptance).