Quite the opposite in fact. Instead of air traveling under the car, it hits the firewall, and gets trapped in various low pressure zones under the hood, causing turbulence, and drag. Many, Many Racers will tell you that they lost a few MPH, and a little ET after removing inner fenders.
Unless this is a fiberglass body shell, with extreme aero /ground effects...it would be fairly pointless to remove the inner fenders.
header clearance would be about the only reason i could cite.
I'm lost in the combination of retaining stock suspension/steering with a back half, and 12 point cage, but to each their own.