Run the numbers first. I would not refi for the same interest rate, just make extra payments to principle. IF you are paying PMI, I would pay to have a market assessment to remove it pronto. Based on the increase in market value, your LTV should be greater than 20%. The assessment should be 400-800 USD depending on location. Contact your mortgage lender to find out the next steps, as sometimes you don't even have to pay out of pocket, they add it to your loan.
Then take the money you are saving on PMI, and put that towards the principle, and invest any extra, assuming you are already maxing out retirement contributions.
Personally, I do a hybrid of paying down mortgage and investing. I refinanced from 5.8%/30yr to a 3.5 %/15yr. I was already paying an extra $200 on principle, but the refi saved me the same amount, so I used the savings as the "extra payment" on the principle and am investing the $200.