30-20 psi wont work for a nice pour. I personally set my beers to 30PSI for two days( it just gives a nice start to carbonation, so if I'm desperate, and can choke a few down.) Then back down to around 12-15 psi to top up. I am by no means experienced at brewing, However it is better to keg condition consistently at a recommended PSI as it can take time to keg condition. I think if there's an idea of a high PSI is to ramp up the saturation and it may just be troubleshooting.
If you are set on having a balanced system, then serving pressure can vary, based on your line length. You can still serve a low carbed beer, at a low serving pressure on CO2, If line length is adjusted for then serving pressure is a moot point. or if you need a longer line length, you can push with nitrogen, which will keep the pressure in the keg consistent, however not alter the beer carbonation too much.
Had a few, may not be well written, but I think it corrects a few items.