Does the code allow for interceptors that modify variables outside of HP/speed etc? For example, a unit with an improved radar system that lets it fire weapons faster and more accurately. Or a stealth craft that has a better chance to dodge enemy fire when you select aggressive interception mode. Rotary launchers/multiple ejector racks that let the plane carry more ammunition than normal also occurred to me.
On a somewhat related note - can research projects affect these variables. You could have a Top Gun dissimilar air combat training (DACT) program that makes your pilots better. It could either add the bonuses above, or give an extra 10% speed as they hunt the aliens more efficiently.
As a final question, could there be craft with built in special weapons unique to them? An F-89 cleared for the genie air to air nuclear tipped rocket, or swarms of rockets, an F-14 with extra long range Phoenix missiles. (I am aware that we try to avoid real world craft, but these were the first one weapon one plane systems I could think of.)