"Buy down" interest rate on Primary Residence or keep rate

Hi Guys, I was wondering what your thoughts are on "buying down the rate" vs keeping it slightly higher.  My growing family is in a condo currently at 3.875%, refinancing us to 2.75% is in process.  To "buy down the rate" to 2.5% would cost us $700 and take 2 years to recoup the cost.  We may be selling/moving in the next few (2-3) years so we're not completely sold on buying down the rate.  We are also not sure if we are going to rent it out or sell completely at that time.  Appreciate any and all advice!