Sorry, i misread the rules, allow me to revise my findings.
Not only do they earn 2 points for landing troops, they also earn two points for BOMBARDING THE PLANET. so each cruiser can earn 4 assault points a round.
Also the Barge can be an exterminator without replacing it's prow weapons, and activates on a 3+
If you can't AAF with your fleet enough to get into low orbit with your superior armor and speed, maybe you should reconsider your tactics or fleet composition.
Also, in low orbit, it is a righteous pain in the ass to harm other ships, considering everyone suffers column shifts and some weapons simply can't be fired. Bombardment cannons obliterate ground defenses something fierce (that whole "defense" status is a real killer).
yes, for every 500 points you lose 1 ap. When you are ranking up 4-16 a round, though, i don't see it as an issue.