This might already be in and I'm missing it but....
Once another empire has given you trade access, you should be able to see the demand (i.e. the stuff in the wealth tab) for each of its populations (or at least the ones that your civies can reach).
Off hand, I can think of two ways to do this:
1) Have more special tabs on the intel (ctrl-F5) screen that present the same info as on the wealth tab of the population (F2) screen.
2) Allow access to other races in the wealth tab of the population (F2) screen. So if the Blarg have granted me trade priviledges and the Cetans are at war with me, then I'll have both "Terran Federation" and "Blarg" available in the F2 pull-down, but I won't have the Cetans. Switching to the Blarg shows me all of their populations (in read-only mode), but all of the tabs except "wealth" come up blank.
The reason I like this one is that it seems an easy generalization of SM mode (you've got two modes you can be in rather than three (SM and normal) and the new mode has even fewer permissions to do anything than "normal" does), and it's easily generalized to higher levels of treaty. For example, getting access to tech might let me see the Research tab, while full alliance might give me access to all tabs, along with (maybe) the F5 and F6 screens.
You might also couple this sort of thing to espionage teams, e.g. an espionage team on a planet might unlock access to screens that are more protected than the current treaty status.
BTW, I noticed someone mentioning a while back that failed espionage attempts should have a negative impact on diplomatic relations. With the new point system that should be fairly easy to do - just treat it as a negative event.
John