Look at http://wam.umd.edu/~jcd/Destabilization.bmp
It's a picture of the money spent on the Yor to be destabilized, and for both espionage and destabilization, the values are more than double what I'm spending on them! Whoever was wondering whether the alien races ever spend on destab/diplomacy, THEY DO. In the particular game I'm playing, the following background choices would compel the Torians to spend extensively on Yor destabilization (and I guess espionage too):
1. The Yor somehow cut a huge deal with the minor races or something to get an incredible amount of money in the middle of the game. They got rich and started to produce a monsterous military of Dreadnoughts. So monsterous, in fact, that their military is the strongest in the Galaxy.
2. Their economy, influence and morale are terrible.
3. The Torians are Friendly with me, I'm at war with the Yor, and the Torians have been at war with the Yor in the past.
4. The Torians have the second highest influence in the galaxy (except mine) and their systems reside physically closer to the Yor's than any of the other races' systems.
5. The Torians fear the Yor military, preventing them from declaring war (I tried to give them all kinds of stuff and they just wouldn't do it!) The Torians are technologically advanced, but I permanently eliminated their military might and their top 3 military-producing planets with Terror Stars during a previous Torian-Terran war. So they WANT to help me beat the Yor, but they have so few ships that they must seek alternative methods to overcome the Yor, rather than declaring war and getting themselves conquered.
The Drengins are the only other civilization left, and both of the minor races left are insanely in debt because they cut tech trade deals they couldn't handle LOL
I don't think the Drengins would dare destabilize the Yor, since they are ALLIED with the Yor. I still find it odd that the Drengins never declared war on me even though I fought their allies, the Yor, for about 7 years. Must be because I have a few powerful ships and they are afraid of me. I have like 14 Avatars and 3 high-rank Overlords and the Yor have 120+ Battleships/Dreadnoughts/Combat Transports that are giving them a negative income but their treasury, like I said, is still enormous. I suspect they traded techs to one of the lagging minor races, because one time I tried to trade techs to a minor race and he had them all!, but I had been trading techs to the Yor early in the game.
Long post, but the screenshot, for me, is revealing of the AI's behavior.