I drove mine for around 3 months sans front shaft due to a noisy diff. As you say, loss of drive to the front was certainly noticeable when driving briskly in corners.
Upside was a lot less driveline backlash (manual transmission) and a slight gain in fuel economy on the freeway.
A part time kit would also include (un)locking hubs which would further reduce drag on the front. Just pulling the shaft sees the axles and diff still being 'driven' by the front wheels.
What about modifying the airbox for better flow?
There is plenty of info around for mods upstream of the filter, but I think the outlet from the airbox is ripe for improvement. I haven't measured the throat area but it certainly looks like a choke point to me.