I've been thinking... rather than have perked planes either available or not, why not perk the capability of the plane.
For example, if a perk plane costs 70 points, and you have the points to fly it, you get a full up round with 100% capability. But if you don't have the points, you can still fly the plane but it has limited fuel or limited ammunition or absence of WEP or a faulty engine that only gets it up to 80% of it's cruise speed or some other limit.
Whaddaya think?