Question about velocity stacks and airbox mods:
Would modding the airbox increase the intake howl?
It certainly could increase the howl depending on what you do to it or by replacing it with velocity stacks.
FWIW, I used to believe that more howl was positively correlated with increased flow. I don't believe this any longer as both may be completely un-correlated.
You may also be damaging your engine in the process for little in return. Also: unclogging the exhaust produces more air-intake as a by-product.
As stated by @philb
...if it ain't broke...