You can buy down the rate, and deduct it on your taxes. I'm not seeing sub 4% anymore either. With the higher prices and the rising rates, it's tough to find deals in big city areas.
I will say I am amazed how much rents have risen in the past few years. My first rental of three years, has gone up $275 in about 2.5 years. I still charge below market, no vacancy issues, always filled.
Same thing with another rental. In the 1.2 years it's been a rental, rent has gone up $200. I still charge below market rent there as well, though will be raising it next year IF I don't move back into it.
If they keep rising like this along with prices, I may very well refinance to draw some cash out and pool for another market crash or some assets elsewhere.