Atnas, I too have a wraithunit from hell. It's very expensive. I believe that Eldrad should take Divination powers, only because he gets so many opportunities to get the good ones, and they can be especially good when used together. I have another farseer that I use with Eldar powers. He uses Doom and Fortune, as Guide can be replaced by Prescience (which if Eldrad has, he can cast twice, at better effect than Guide anyway), and I don't think that Eldritch Storm and Mind War are powerful enough to keep me from trying different powers. I like Divination for Eldrad, and I use it this way: Ideal spell list for Eldrad is Prescience, Forboding, Misfortune and Perfect Timing, though the last one is not essential at all, and rarely gets cast.
Here is my unit composition:
10 Wraithguard (Spiritseer, Enhance)
Farseer (Doom, Fortune, Spirit Stones, RoWit)
In the turn before this unit were in danger of being charged... even by an uber unit, here are the spells I cast: Doom and Misfortune on threatening unit, Prescience, Fortune and Forboding on the Wraithguard (oh, and I also have a Wraithseer (double FOC), who casts Deliverance on the Wraithguard... for giggles).
Here's what happens: [Note, I think I'm okay describing effects, as long as I don't state what the source of those effects are. If I'm wrong, please edit.] Wraithguard are an amazingly tough unit, especially when they benefit from Fortune, and the Baron's boosts. Adding Enhance makes them an even more effective unit in an assault.
If I only had one farseer, or just Eldrad, I would take Eldar powers, because Fortune is absolutely essential to my build, but I run two, and if I had Eldrad running Eldar powers, he wouldn't use many of the powers, and probably just cast Guide, Doom, and Fortune multiple times. Using a regular farseer, even one with stones, on the divination list, I would take Prescience, and then my final power would be an absolutely random spell, some of which are useless to me, either because I already have that effect, or because it's not useful without another spell on the list (which I couldn't get). If you're trying to build an army around a BRB spell list, Eldrad is essential, as he has the best chance of getting what you want (and the ability to cast it all). But, like I said, Fortune for me is essential. I don't open my case without it.
Also, I think Telepathy is junk. They all sound cool, but most of them rely on the opponent's leadership, and I have found morale effects to be underwhelming in 40K, given that everyone is either Ld 10, Fearless or And they shall know no fear. Also, the last two are two charge powers (and don't seem worth it), meaning that even a farseer with spirit stones is tapped out on one spell, and Eldrad only has room for one more. Even Psychic Shriek is poor compensation for those other junk powers.
I've been running an Ulthwe list for a looooong time now, so many farseers with interlocking powers is my bread and butter, and I really think that divination and the eldar powers work very well together for those willing to invest in lots of farseers.
[mod]There was too much description regarding how Fortune and Enhance work in relation to the forum rules on copyright. Post edited accordingly - Iris.[/mod]