Just a couple things that might enhance immersion, and probably the giggle factor.
Accurate flap systems modeling. Some aircraft had a flaps switch that would deploy them as long as you held the switch/button down. Others had pre-set settings (ala Spit), while more had a fixed graduated system like we have now. Fiddling with these would actually be fun.
"Doohickey" modeling. The P-40, for example, had a warning horn that screamed in your ears if you tried stuffing the gear down with the throttle forward. The F4U had a pre-stall warning light. The Ju-87 (early marks) had that screaming siren. Again, it might be fun.
Landing gear enhancements like accurate gear retraction sequences and actual, working shocks. Not only would this provide a bit more realistic ground handling, but you wouldn't see the gear retracting through an already closing gear door. The F4F was noted for rather drunken handling on the ground with such soft shocks, while early marks of the F4U bounced around like Tigger.
Built-in toe brakes. Hit a stick button or key, kick the rudder, and you get differential braking. It'd also be nice if there was an adjustment slider for brake force somewhere. Using a stick button for brakes instead of pedals means you can't vary the brake force.
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Flakbait [Delta6]
Delta Six's Flight SchoolPut the P-61B in Aces High
