Should I refinance my mortgage or stay with what I have? (Please keep in mind that a mortgage is paid monthly not annually)

Current Mortgage Scenario
Balance	$350,000
Years left	21
Annual Rate	6%
Payment	$
Proposed Mortgage Refinance
Payoff balance	$350,000.00
Refi Costs	$5,000
New Term in Years	30
New Annual Rate	4%
New Payment	$
What is the monthly cashflow savings? $
If I put $500 per month of that savings into a Roth IRA every month for the next 30 years earning 9% per year, what would my nestegg be at the end of that period? $ Should I refinance? Yes or No