The Borla is well expensive. You should be able to have a custom exhaust fabbed for the vehicle for a lot less money.
It is worth some HP but not a great deal, most HP comes from scavenging on a n/a setup which require long tube headers. A better Y pipe and cats will also make a difference, but hay I guess thats why its called an exhaust
system rather than just a component.
P38's use exactly the same basic engine, heads, intake they are just larger displacement if you have the 4.6 the same bolt ons will work just as well.
Better intake with a CAI and FULL exhaust including headers. Cam and heads would be next up. Or some even rip out the EFI and run a 4brl carb instead. You can even ditch the air suspension for regular coils if you want although depending on use it's not needed. 280bhp should be easy from the 4.6 with 300bhp possible although it's be a bit wilder.
If the air suspension is playing up and not working properly it's usually water in the system. The compressor produces water as a by-product, as all compressors do. But most people don't ever drain the water away and sadly this includes most of the dealers. There should be some drain plugs you can access then I think you just need to leave the vehicle for 30mins to an hour with the engine running and it usually sorts itself out.
A service guide should expand on this, or I'm sure there's a writeup somewhere on the net.
