I think the AI's response to a galactic economic boom is a bit careless.
It frequently happens that there is a economic boom increasing the tax revenue of all races. The AI usually uses this extra weath to build ships/buildings (mostly ships i think) and thus increasing its maintenance costs. For as long as the economic boom lasts, that's not a problem. However, when the economic boom is over the AI players are usually left with more expenses than income (sometimes a balance of -2000bc per week or more). The result is that their economy always crashes after an economic boom.
There is nothing wrong with using the extra money, however, the AI needs to be a bit more carefull not to create a large drain on their economy while the economic boom lasts so it doesn't crash afterwards. It certainly makes them vulnerable and a human player can take advantage of it.