I have 1/2" copper pipe in my garage to distribute compressed air around the shop. I tried to keep all the fittings and valves full bore right up to the final connectors which are 1/4NPT. I'm in the process of shopping for a new compressor that is better able to handle spray guns. What I'm finding is that until you get up to the massive 80 gal industrial compressors, they almost all have 1/4NPT tank outlets and regulators. It seems odd that they wouldn't size that up to at least 3/8 or 1/2 to get the most out of the system.

Am I looking at this wrong? Doesn't the initial restriction out of the compressor matter?

I’m sure more knowledgeable people will chime in but you can put 3/4 pipe but it won’t matter if you’re compressor doesn’t kick out enough volume to supply that. It may pressure up the system but if you use multiple tools a small compressor won’t keep up with the volume being consumed.

You can get approximately 5cc per foot volume through 1/4 tubing, 13.7 through 3/8 and 30 through 1/2. Line length, temp, bends, restrictions, Reynolds factor, supply pressure, return pressure and a bunch of other stuff play into it but those rough figures will give a rough estimate of volume per foot in each line size.

^^^

I understand that, just don't want to lose any capability that I don't have to.

Putting a tank to hold volume somewhere in the system should even out your flow issues.

A lot will depend on your equipment requirements - HVLP needs high volume, so larger pipe will feed it better. A lot of paint guns still have 1/4" fittings, but having a store of volume close to the point of use can help.
Rather than replace the pipe with larger, I'd run higher pressure in the pipe & have a regulator as close to where you're spraying as possible, even at the gun.