My recommendation is to reduce the pressure in your tires to the minimum you expect to use and then see if your existing unit will bring all four of them back up. In your driveway of course. If it works and you aren't hankering for a new toy you could call it good. I have a $60 portable 12V compressor; the one with the jumper cables and fluorescent lights. Not the unit to give me a lot of confidence on an expedition, but that little compressor surprised me. At a wilderness trail head I loaned it to a horse packer with a completely flat tire. He needed 80psi and darned if my inexpensive little unit didn't sit there and pump away until he got it all. It took at least 30 minutes, but it had power left over and didn't get very hot. I was impressed.
My current truck came with a small tank and compressor built-in, install by the previous owner. Very handy.