The starbase rush is an Illum counter on smaller maps. Basically, the idea is to get a starbase to THE critical planet that two people would be fighting over early. Get the starbase up quick and early, and you just took away a huge planet from your opponent. Outside of scout spamming against a PURE illum spammer, this is probably the best option ya got. And it only works for Vasari and their mobile starbase.
DUDE, to set up that starbase in time you have to aim for it before you even know what your enemy is doing. You need funds ready cause it lolass expensive, you need research done. To counter an illum spammer with a fast forward starbase you have to go for that starbase before the enemy has even decided he's gonna spam illums.
That's the part of this tactic that makes me decline it as a counter. You don't KNOW what the enemy's gonna do, but since they ALL go illum spam, you know this particular bloke will do it as well.
That's not a counter, that's scrying 
A counter is when you see an enemy with something and then you produce and bring something that defeats what the enemy has. Like flaks and fighters vs. carrier spam. You may lose the first battle but the second is yours. Then it's the enemy's turn to counter you.
With illums, you have to counter before you really know what you're countering.
That's why this is NOT a counter.
