I like playing Eldar (Ulthwe almost exclusively) and I do find them quite punishing to play, particularly against more experienced players. that's not a criticism of the list though, more of myself

They're very sensitive to deployment and BMs, so often for me the game is lost before I even start

The lack of Leader is a bit of a bummer, would that upset things too much if Farseers, Exarchs and Autarchs get them? Or would that make fms with those too cheap?
Difficult to comment on other units as how each unit is used (or it's individual stats) are so tied in with the "Eldar way". Scorpion seems a little undergunned (on range mostly, 60cm feels short), but then again it is a skimmer with 25cm move and does have the Hit and Run rule. Cobras are difficult to use, but potentially awesome, but I would agree that Void Spinners are the best SHGT. Though that does depend on who you're using them against - vs. Marines they're okay, vs. Guard they're awesome. Same could be said about the Scorpion though (though the opposite).
Only used Warwalkers once, where they got shot to pieces. Bit too expensive to use them that way (Rangers are much cheaper and just as effective a road bump) but I'd probably try them again as suggested above.
Fireprisms - very useful against Guard, much less so against anything else. Don't forget that a full 6 unit fm is 375pts, so you would hope that it would be effective. Most people would take at least 1 firestorm per fm though and they are VERY fragile. Might think about taking 6 unit Falcon fms though, might make them survive a bit longer.
My favourite unit is Guardians+wraithguard - I've never failed to get my points back with them, even as foot sloggers.