Laz,
Making these slightly better aircraft that much more expensive certainly does have the effect of making fights against them boring and irritating. Maybe if people were willing to actually engage in them they'd be fun to fight.
I personally don't see a real significant difference between fighting an La-7 or a Tempest, an Fw190D-9 or a Ta152H-2, a P-51D or a Spitfire Mk XIV. If I'm in a 1940 or 41 aircraft, I am going to use the same tactics against them and am going to be horribly outclassed.
Making the perks priced more in line with their performance wouldn't make top end aircraft much more common, like the F4U-1C they'd still be rare. In addition, who is to say the "Bob" the Tempset pilot would be flying a C.202 if here weren't in a Tempest? More likely Bob'd be in a La-7. Not much different.
Fatty,
Most people can't earn an F4U-1C in a single flight. I've done it, but not very often. Some people have trouble earning an F4U-1C in 8 flights. Do you really think that the perk prop fighters are that much better than the top end free fighters?