Guard posts will never work. First of all, they aren't mobile. Most maps have wide open spaces and there is not way you could cover all enterances to your base with guard posts by the time they attack. Even if there was only one enterance that you manage to defend in time, there is nothing stopping them from rushing past your guard posts. Once they're out of range of your guards posts and gutting the soft underbelly of your base, you're pretty screwed. Secondly, guard posts aren't really all that strong. Granted, I've seen them shred units early in the game (microwave GPs that is,) but unless the number of enterances to your base is limited, you'll never have enough firepower to stand up to any reasonable sized army. Remember, your leaving you enemy with all the mobility and they can choose exactly where they want to attack. GPs also cost more than lynxes so you could be wasting valuable ore. If placed right they *might* help though, but then, that's time away from building other structures with your convecs. Besides, stickyfoam outranges lasers.
EMP missiles aren't worthless against meteor defense. Just worth less. Meteor defense can still miss, and I'm pretty sure it can only target one missile at a time. Plus, just the threat of missiles means Eden has to waste a lot of resources on defense. Meteor defense doesn't come cheap. It takes a significant number of workers and scientists and costs rare ore too. Plus it eats up a lot of power. Not to mention, if their observatory ever goes offline, like whenever a scientists dies, none of the meteor defense systems work. Now, with all that being considered, meteor defense can only really be used to defend a base, and usually only important parts of it too. It does nothing to help defend an attacking Eden army out in the open. Granted, you can largely move out of the way and save at least most of your vehicles from being disabled, but that's not always so easy to do with Tigers.
And scouts aren't worthless in multiplayer. They are a cheap 250 ore detection system that will warn you of sneak attacks. They probably aren't very useful, but for 250 ore, it probably doesn't matter much. And even a few extra seconds of warning can save you quite a bit. Plus, turn the headlights off and you have sneak detection to find their sneak attacks. Light towers won't tell you about approaching vehicles and I don't think they reveal them on the minimap either. (I could be wrong about that, but in my experience they never seemed to.) And yes, I've had a few attacks (not quite) foiled by scouts. I was able to cut a nice whole into a base but the early warning stopped my from being able to destroy as much as I'd have liked since they were able to reposition their army in time.
I don't believe double universities and nurseries have an impact. I think it's just the greater your population, the faster it grows. (Maybe I'll look into exactly how it works sometime.)
And as for giving Lynxes enough room to manouver, it doesn't matter much unless you can either outrange the tigers, are avoid them competely. It doesn't seem too likely you'll outrange all the weapons they have and running around isn't all that effective either most times. Keep in mind that to run around them, you have to cover more ground then they do to get in your way again, so the extra speed almost doesn't make up for it.
And yeah, the extra fire rate really makes the Tigers well worth their money as far as attack power goes, not to mention the extra hit points and armour. And yes, Acid Cloud really is quite effective against spiders.
