I probably wouldn't. It will save you $21000 over 30 years if you keep the loan for 30 years. But, you want to pay it down sooner making it less attractive. It could also cost you money if you move, refinance, or pay it off in under 5.5 years. You also have the lost opportunity cost of that $5k. For example, $5000 in an index fund earning 7% per year will earn you $33000 over that same 30 years.
Exactly (at least the last part. I disagree that it would save 21k). It is tempting to do the simple analysis of the OP, that apparent future saving , when the correct way is to consider 2 different cashflow forecasts, one with, and one without, the decision to buy a lower fixed rate, with a range of assumptions. This way you include opportunity cost of capital, taxes, etc.
ie. On top of that, the rate could drop, meaning you could have refinanced at the rate you purchased for free. It's a one-sided bet. And an expensive one. Even when you "win", you loose money and give fat fees to everyone as a result.