I have personally seen, and changed the gas tubes on, SBR's that have had reliability issues from gas tubes caked with crap. Granted, these were police guns (Pierce County SWAT) that saw many times the number of rounds an average shooter would put through a plinker.
A shot of brake cleaner or other solvent and a long pipe cleaner is all you need. Takes about 15 seconds. Then a couple of shots of compressed air and you are good to go.
For just random plinking and shooting less than, like, 10,000 rounds a year, I would agree you don't need to clean them.
With a lot of .22lr going through them, I would recommend it.