Which is better: a 100% bad decision, or a 60% bad decision?
Answer: Neither, they are both bad decisions.
The interest payment deduction is the biggest scam in the history of the USA. It makes you think that paying a lot in interest to banks is actually a good thing, when it is a bad thing in reality.
One figure that matters most is the total interest you pay for your properties vs. the principal over the total period you own them.
The banks and most realtors have a big incentive to have you pay the most interest possible over the life of the loan. Banks are the direct beneficiary. Realtors get higher commission payments for higher property sales, regardless of how much interest you pay. That's why many, if not most realtors try to get you "the most house that you can afford", meaning the highest possible house price at the maximum allowable monthly payment you have been approved for. That's why 30 and 40+ year loans exist. There is no rational reason why it should take 30+ years to pay off a house. You will always be paying more in interest than you do in principal with these loans, and at a higher interest rate to boot.
If you refinance your existing loan that has excellent terms, then you are paying loan origination fees to get something worse. Is that a bargain? To pay extra for something worse is a bad deal, period.
I can't tell you whether it's a good financial decision to buy a $200,000 summer home. That depends on how much free cash and income you have above and beyond your current mortgage payment. It also depends on the true market value of the summer home vs. the price you pay, as well as any continuing devaluation of the price in this market. As a general rule, I think you should be able to afford sufficient payments to pay off all your mortgages in 8-9 years, with 15 year mortgages. I doubt you will hear this recommendation from anyone else. That's because the goal is to reduce the total amount of interest you pay, which is only in your best _interest_ and contrary to everyone else who is trying to make money off of you.
For example, if you make a $3,000/mos payment on your current house, it will be paid off in only 4 years. It will cut the total interest you pay vs. the 9 remaining years by more than 50%. That will save you about $20,000. The extra $1,800/mos you pay (approx) comes to about $87,000 over four years.
Will you be more financially secure with one house that's paid off in 4 years, or owning two houses with a large mortgage with another 11 years remaining? If you lose all your income, which option will most likely result in foreclosure, eviction and bankruptcy? If you don't buy the summer house now, do you think they will all appreciate tremendously in 4 years, with the fresh memory of the recent real-estate crash? Or is it more likely that the prices will fall some more and then stabilize for a while before more slowly increasing than the last boom that was caused by massive speculation and easy credit? Look at the number of interest rate resets that are still pending to occur in the next four years. There is a large number of foreclosures still waiting to hit the market.