I just thought of something a couple days ago that would do a lot to get humans out of the base. Usually humans just camp because:
- They know they'll get mobbed if they leave
- They aren't confident in being able to accurately hit aliens like marauders and dragoons before they get eaten, so they need to be able to retreat into the base quickly
What I would propose is a stage 2 item called the Cloaking Device. Like you probably guessed, it makes the wearer 95% invisible to enemies, and 50% invisible to teammates (so they can still see him, but can recognise that he's invisible.) The cloak would last 30 seconds and then would take just as long to recharge. Also, the cloaked player would still show up on alien radar, however the alien needs to be twice as close before the player gets registered on the radar. And finally, the cloak automatically shuts off if the player either fires his weapon or starts taking damage; after he stops shooting/taking damage, the cloak takes 5 seconds to fade back to full capacity. Oh, and the unit would cost about 300 or 400 credits (yes, pricy), and all other upgrades on the player will NOT be cloaked, so the player needs to have no armour in order to be completely cloaked. This would resolve balance issues later on in the game.
What this would allow is for humans to, in a way, immitate the gameplay of the aliens. They would be able to leave the base, and stay relatively undetected. Even if they are discovered, they would be difficult to track and kill. And, to prevent the cloak from being abused by humans, it's expensive, using armour in conjunction with it makes it nearly useless, and it only works in 30 second bursts. The only problem I can see with it would be that, if the player still shows up on enemy radar, aliens can just follow the blue dot. Since the player can't outrun an alien, he can't escape radar range. However, removing him from radar altogether would be overpowered.
Wait, I've got it... the blue dot only appears in blips, in 3 second intervals. The three seconds gives the player a chance to escape. Also, when immobile, the player does NOT show up on enemy radar at all (until their cloak runs out of power, of course).
Orrrr the cloak device could come with a "Decoy" feature. When the cloak is activated, your radar position is frozen to your current position, and your real location is invisible until the cloak is powered off, at which point your "frozen" position disappears and aliens can properly track you on radar.
All in all, I think a cloak would encourage humans to leave the base. The only thing I'm not quite sure of is how the radar should work, but that's only a small part of the idea.