Dad,
Ken is right, much depends on how long you have been there and what your goals are. What is the right amount to trigger a refi?It differs for everyone. Some people will refinance if it saves them $50/mo, others need to see $100 or more. It depends on your financial situation at the time. Do you want to see the balance go down or have more money in your pocket monthly? etc..
With many of my clients I don't just automatically put them in a new 30 yr fixed. If you have been in the home for 4 yrs at 5.5%, I will show the client a 25 yr fixed at the lower rate. This usually still lowers your payment but does not 'restart' the amortization clock back to 30yrs, in which case you pay much more int. all over again and it also cuts a year off of their original term, thus saving interest paid. The 20 yr fixed also works perfect too. It depends on your situation.
Ask yourself what is most important at this stage, monthly cash on hand or building equity? If having more money in your pocket is what you and your family need and you do have a substantial chunk of equity in the home alreay a new 30 yr at 4.875%-5% with only $1700 in closing costs (lender and title fees)is not a bad solution if it frees up over $100/mo for you, you will recoup that cost in less than 2yrs. If your goal is to pay off the home before you retire or to have a low balance in the 10+ years you will stay, then entertain a new 20 or 25 yr fixed loan at a lower rate.
Dan