Is a refinance always a good idea?

[Cosmo Iannopollo]

My situation right now is that I'm house hacking a two-unit multi-family. Over the past 2 1/2 years, the market has appreciated slightly and my wife and I have done modest improvements to the house. As we consider our next move, a refi seems like a good idea, but I'm worried about how it will affect the cash flow of the current property. 

Are there times where a refi is a bad idea?

Stats of my current home:

Current mortgage owed: $187,000 with 3.25% interest rate

Monthly PITI (with PMI): $1,475

Rent Unit 1: $1,200/mo

Rent Unit 2 potential: $1,200/mo

Right now, these are at the high end of rents in the area. Once we move, we'll gross almost $1K/mo. 

Thoughts?