You should be able to trade intel gained about a civ to other civs, have the value based on what it is. For instance if it were troop locations and they were at war the other civ might want that and would want to get it, city information would be valued low as it is easy to get, and so forth

! :) !

I like this idea. What other types of intel were you thinking of?

Also I think that troop locations should last until the specific unit moved instead of everything dissapearing after 1 turn.

To make this more useful, spies and intelligence would need to be more valuable in the first place. But I think this idea would be great under those circumstances.

I know it would probably be really complicated to this but, I think the intelligence side of the game needs some serious revamping. Right now its pretty damned basic. You put a guy in and you automatically know what units they have and for a price you can find out where they are for a turn. I seriously doubt thats how the world works, or else the NSA wouldn't be larger than the CIA.
I think the intelligence aspect of the game should be comprised of several different areas, those areas being Human Intelligence (Spies), Electronic Intelligence, Signal Intelligence as well as good old image intelligence which could be either Spy Planes or Satellite.
When it comes to Statellites, I'm not thinking that once you put a bird into orbit you can see the entire world, rather with each satellite you choose (or have your advisor choose, depending on the options toggled) to pick various targets an the satellite alters its orbit to see it. And if say you have 5 different satellites up there they can view 5 different targets and so forth.
For the Spyplanes, that should be a unit that each nation could build, first a U2 type plane and then maybe the SR-71.
For the signal intelligence, in order to make use of this you'd have to set up posts through out your territory (and perhaps through treaties on allies territories) that can pick up enemy communications. Or if your like Canada, you could set up a place like CFS Alert which thanks to its geographic position can pick up a lot of stuff from around the world (I think its limited to the Northern Hemisphere though, which makes sense. Of course if you're using another nations territory you'd have to share the 'Take' with them.

And to expand on that thought, while the electronic intelligence is a pretty modern phenomenon, spies are almost as old as history itself. Human intelligence is the obvious one, but even Caesar received encrypted messages from spies all over other empires.

I'd like to see spies become an evolving concept, to even a quarter of the extent that military evolves. Spies should not be constrained to a "yes/no" question.