After Refinance - to pay down primary residence loan or reinvest?

[Robert Duffer]

I recently found myself in the process of restructuring my finances to rekindle my real estate investment goals.
I currently have a single family home (with a decent interest rate) rented in Annapolis Maryland. I've been living in Seattle Washington in a home with an interest rate higher than most because my house (given the current market) is worth less money than I owe (about 45K diff). In the past I did not see the logic in refinancing to dig the hole deeper via refinance closing costs (10K deeper) if I was not planning on staying in the house long term. However, I recently refinanced from 6.75% to 4.3% at no cost whatsoever given the new refinance rules (HARP). The new loan amount remained the same and no closing costs so the hole did not get deeper. This obviously makes for a smaller mortgage payment hence my question is this...do I continue paying the old "larger" amount (which I can afford) in order to close the gap loan to value on my home? I'd like to be able to sell it (break even) at some point - or do I take the extra cash and invest it elsewhere? (i.e. save it for a down payment / invest on a new property opportunity).

Thanks in advance for any advice / feedback.
- Rob