Are you sure that you were on the same level of elevation as the wounded soldier? From memory, even if you are like one step down from the wounded soldier and right next to them you still cannot heal them. The same goes for stunning i believe. I actually find seekers a bit of a joke, and over watch is actually (IMO) the best tactic to kill them (excepting throwing a battle scanner, which is the best way). When you trip them, bunch your whole squad up behind cover close together and stick them on overwatch. When the seeker de cloaks, it will get a barrage of shots and be killed. Keep overwatching until they are all dead. Simples! I am of the opinion that the base assault should always be done immediately after you get armour and lasers. The reason why i say this is that the only hard counter to elite mutons is a mind controller. 3 elite mutons can be a real pain in the arse if you dont have an experienced team. In order to effectively counter them you need a psi soldier, and for that you need base assault. By the time you have built the psi labs and found a soldier and levelled them up, you will probably be at the point of elite mutons. They can do a ton of damage too, much more than regular mutons. Its possible for them to outright kill a soldier wearing ghost armour in one shot. Because the base assault scales with where you are in the game, there is not really much benefit in waiting. The only thing that changes is that you have to deal with sectoid commanders in UFO's instead of overseers (and get through the mission of course). For that laser weaponry is sufficient.