Warwalkers are very efficient units. I love mine, all with twin scatter lasers, they rip apart even marines reasonably well, if guided and doomed 
How are you finding guardians? I really struggle to see why I would want to use them, they end up being just wound counters for one horribly inaccurate heavy weapon.
You've contradicted yourself to a certain extent here, in that you're singing the praises of War Walkers armed with Scatter Lasers (rightly in my view), yet Guardian squads can perform a similar fire support role when equipped with a Scatter Laser, and it takes more fire power on your opponent's part to neutralise a Guardian squad than one War Walker, for example. The Guardians also have the advantage of being able to score, which is important not to overlook.
They are only wound counters if you use them in that way. You can't just hold back against all armies throughout the game, as this isn't playing to the unit's strength. Being able to move and fire a heavy weapon is their bonus. Other Eldar fire support infantry, such as Rangers and Dark Reapers, don't have that luxury. The idea with Guardians is to soften up the opposition first with other units, and then have them move up in support. Will it always work? No, because Guardians are fragile, and are vulnerable to certain types of attack which are difficult to protect them from (deep strikes being the most obvious), but it's always worth considering, as Guardians need not be immobile 'wounds' as you put it, that's just one (inefficient) way of using them.
I need to assemble and paint lots of Dire Avengers if I want to field them as a true Biel Tan force.
No you don't. Never was there a more false representation of how Eldar craftworlds are comprised than the third edition supplementary craftworld codex. For more details take a look
here. In fact, Biel-Tan is the craftworld which is closest to what you might call a 'vanilla' concept, i.e. as long as Aspect Warriors are in the majority overall, it doesn't matter which other unit types you field.
Definitely looking at the codex, guardians don't seem to be worth the points investment. I was never overly fond of them with the old codex, other than the fact that they were a better choice that Dire Avengers.
The only issue is the range of their Shuriken Catapults is six inches too short. I've play tested them extensively with an 18" range, and it solves all of their problems. For ways in which to use them see my comments above.
I'm hoping that 6th edition will give Eldar a little boost. Hopefully they'll be one of early Codex for 6th as well. It's been a while since we've had a new book now. One of the oldest if I'm not mistaken.
I beleive they are the oldest 4th edition codex still around Delthos.
The Tau codex is definitely older by a few months. I'm also pretty sure that the Black Templars codex is the oldest of the current crop.
Nicholas Bies: I don't write army lists for people, as it isn't of much help to impose my play style on others. Build the list that you think you would like to field, and I'll offer advice accordingly

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