The Intelligence Levels portion of espionage is foolproof now, yes.  Prior to the 2.0 patch you had to have spies on the planets to gain intel levels...a VERY costly endevor, just trust me on this, I'm a spy-nut.

Planetary (Active) spies however still have their use.  You cannot steal tech w/o a spy placed on a planet (via espionage, invasion tech steal is different than this).  Shutting down buildings such as farms or econ buildings are very useful to detroying an economy or pre-invasion (yeah, 1 planetary spy can kill BILLIONS of people in 1 week....POW).

I'm slightly confused on your last sentance though, can you try to re-word it?

Cold War tactics do wonders, but not economically vs a fleet.  I've shut down the Dregin by cutting their purse-strings.  I hampered them so bad that I was getting spies quicker than them eventually and then had every one of their buildings shut down.  The other AI's then monky-stomped them into space dust when they couldn't make ships to replace those lost in battle.

And yeah...having 100 spies in you're arsenal is by NO means economical.  ~grins~

Yup, the only jobs for spies are as follows:

-Passive spy on an empire to gain intel levels

-Sit in the pool of spies in case an AI plants one on you and then nullify it

-Disable a building and at the same time allow the random number generator determine if you steal a tech

        Actually, that sounds like alot of fun, particularly if you have managed to get a ton of credits, and you have tech trading disabled.  That might be a good way to acquire those environmental techs from the stingy Altarians.

        And I always save a few spies for invasion purposes to disable morale structures.  (or farms)

Also keep in mind that some native English speakers do a worse job posting in their language than you did in a foreign one. Both grammar and spelling seem to be going out of style here in the U.S.