Regarding recasting......most people don't know (or understand) that if you're a few years into your mortgage, and have made extra principal payments, it will take you back out to a 30 year amortization, going back to the principal/interest split of payment #1 at the same interest rate. It does lower your payment, but you are putting a smaller percentage of the total monthly payment towards principal, and the monthly payment is smaller. So the net monthly amount going towards principal is greatly reduced. For this reason we did not do it, and opted to put a chunk towards principal.

Let's say you are 5 years into in a 4%/30 year mortgage. Your current payment is 63% interest / 37% principal. When that mortgage started, it was 70% interest / 30% principal. Do you really want to go back to the days when your payment was 70% interest?

I would only recast if I was a year or two into the mortgage, had a chunk of cash, and needed to lower my monthly payment. It's not a good way to build long-term home equity IMHO. I would try to refinance and put a chunk towards principal to make my monthly payment (and interest) as low as possible.