Just an idea after reading the attacking barricade thread.
1. Acid tubes do damage in the direction that the visible spew travells in, instead of proximity to the tube itself, a fixed-direction turret in other words. The intensity of the damage could proportional to the density of spew particles around a human, so a human treading in a wide puddle of spew from a distant tube will take less damage per unit time that if he'd recieved a direct squirt from a tube placed above a door. In S1 this will be little different from what it is now (because tubes are mostly firing up from the floor) but will allow alien builders to be a little more creative with adv. grangers. At the moment it just feels a little weird when a nearby tube inflicts damage by squirting acid away from me.
2. Barricades can take more damage, heal faster and deal proximity-based damage. Perhaps they could have a single whipping tentacle or similar.
This scheme would give aliens one proximity defense and one directional defense as opposed to the current scheme of one proximity (tubes) and one not-very-effective blocking defense (barricades). The effectiveness of the tubes and barricades can be reduced if this scheme gives the aliens too much of an advantage over humans.
For the humans, another item idea: CCTV, you buy the item and get a small monitor in the HUD. You then place the camera by selecting it and pressing use. The camera is sticky so it sticks to the surface you throw it at, and for simplicity it always points down. The player who placed it can then see a view from the camera through the HUD monitor. Handy for seeing when there's a partially clear path to the alien base. The cameras are small and inconspicuous and don't show on alien radar until they are closer to it than other human structures, but easily damaged when they are found. Humans can buy spare cameras.
Cheers!
-Taiyo