Back in the old days you had pony's and dora's, and pickers, and runners, and ADHD turn monkeys and BnZ'ers.
The difference is you couldn't throw a rock in any direction without hitting a dogfight.
IMHO, you don't have a late war plane dilemma, you have a player density dilemma.
Back then, You could die and get back into a fight fast. There were no shortages of fights. The cost of dying was low because you get back into the action very quickly.
Now you have a painful investment in time to climb out and search and find some action somewhere. I highly doubt anyone flies cautiously because of score concerns. That is a red-herring. They just don't want to have to start all over again back at base. Shorten peoples time to get back into action and you'd see a big difference in loss aversion. Perk their favorite rides and you just increase loss aversion.
Options:
1. Add players. 500 players in the MA solves a lot of problems.
2. Smaller maps. At some point it starts to get ridiculous. If you get down to 128x128 maps, people will wonder if they are really flying a MMOG.
3. Reconfigure to a two sided war with balancing to shorten the frontage thus increasing density for a given map size.
4. Use some kind of capture order to force activity into certain areas.
5. Get on the BBS and stomp your feet and call everyone cowards and timid because they won't fly the way you want.
6. Perk the most iconic WWII planes in the stable, and still not make much difference to the perceived problem of cautious flying. You would probably lower the density some more.