On a Citabria:
Aileron Gap Covers were optional in the 70's. When we redid the Scout, some stick measurements and tuft testing showed that the Gap covers on the ailerons actually hampered their performance. The effect was minimal at best, but why add a part that does nothing? The nose of the aileron is supposed to duct some airflow up and over the top of the aileron when it dips down. Putting a gap seal in there, ruins that design intent.
(Now, the 7 series aileron is state of the art 1944, so, you see why it could use some help.)
Rudder authority on a Citabria is already nice and strong. I guess you can add a little more. Personally, I dont see a reason to.
Elevator does benefit from the gaps being sealed. However, at some point, Bellanca or Champion added them in. Basically, there is a small tube welded to the main spar of the elevator to cover the distance inbetween the Stab and Elevator. There are some gaps in this to allow the clevis bolts to be installed. Taping up one of these assemblies is likely to do very little. The gap that is there is quite small.
Honestly, if you want better handling, I would get the Vortex Generator STC from MicroAerodynamics.
