Refinance car loan, Is it actually worth it or just a hassle?

I've had my car loan for about 3 years and my credit score has improved a lot since I got it. I'm wondering if I should refinance car loan to get a better rate. My current rate is 6.5% and I'm seeing ads for refinancing at like 4-5%. But I'm not sure if the savings are worth the hassle of switching lenders and dealing with new paperwork.

Has anyone actually refinanced their car loan? How much did you save? Did you have to pay any fees? Is it better to go through a bank, credit union, or one of those online refinancing companies?