How about you have a certain (high) chance to run into a crashed alien shuttle.
It's (most of the time) empty, except those pesky spiders (I took it they are pests for the aliens too, right?). So, you get AXP. not really that freakin much, and not that often, but you do, *and* it adds the feeling that yes, Aliens Are Among Us!
Now... add the (lower, maybe much lower) chance of *some* aliens having survived the crash (lvls? Around the lvls of the surroundings, with an outside chance of there being a high-lvl general in there (with his bodyguards, of course))
Loot drop *low*, they are not on a combat mission, so don't carry their gear.
Effect: you want a sure-fire, much AXP and tons of loot raid, you'll still go to the APF or do a city raid. But it gives the low-lvls a chance to get AXP, to see some aliens, to get much more of a feeling that we're under attack.
And RK would be much more lifely with all those chars running around in search of downed shuttles.
Hmm, combine this with *announce* downs ("News Flash: a high-ranking alien general has been downed near NNN, all citizens please help capture it")...
Damn, I want more "we're under attack" feeling. I don't care as much for alien loot... that's not important for RP.