I severely burned my fingers getting greedy with balance transfer arbitrage.
I had been playing the balance transfer game, using 0% transfers and sticking them in high interest accounts (5-6% at that time in Australia). This worked well, and had minimal risk. However, I got too clever for my own good in seeking a higher return. As I had a margin loan against stocks that was at 9%, I figured I could park the balance transfer in the margin loan, "earn" 9%, then pay it back. As I was holding the margin loan any way, no additional risk, right?
Well, doing this through 2008 proved otherwise. Soon enough I ended up with margin calls, and my losses were exacerbated by needing to inject new cash to repaying these transfers. I tried to get too smart, was too greedy and regretted it. If it was doing it again, I'd stick with the vanilla options with no liquidity risk, for a lower return. Given current rates in the US, and the low rate / long term nature of your existing debt, I suspect its probably not worth the hassle.
I have no direct experience with options like peer to peer lending, but I'd view them as an area where you may not recover your money on the time frame you need. Unless you have the spare income to underwrite the risk, I'd be tempted to pass.