A FASS or Air Dog is a good thing if they provide better filtration.
Personally, I went with air mods over fuel so that I run cooler temps and don't have to worry about installing and tuning a wastegate. My personal opinion is that with stock turbos and stock fuel, air is more of limitation than fuel. If you do the Air Dog or FASS and 60 HP (15%) nozzles, you HPFP may not keep up on the hotter tunes. If the pulse width is below 2.0 with 60 HP nozzles, you will likely not have any trouble, but when you get to the 2.2-2.3 PW, it is hit or miss on whether you will be able to maintain rail pressure. If you didn't maintain RP, you could upgrade the HPFP, but the only one I know of without going to dual fillers (which is expensive) is IIH and I have heard way to many horror stories with their pump failing and causing very expensive damage.