Welcome to Librarium Online!
Is it worth it to make them passable in CC by upgrading them?
It seems like they could cause major hurt if they bladestorm then assault.
It's better to Bladestorm and not take the risk in CC. Maybe against IG or Tau they could hold their own, but anything else they'll bounce off even with upgrades. They're than locked in and you can't really afford to have your Troops tied up usually.
I'd leave them shooty, than get in there if you're SURE you will win the combat and it won't screw you over.
I make all of mine shooty and they arent all that bad in CC, better than guardians but they arent howling banshees, if you cant get away in time then charge, your a lot better of on the charge then recieving one.
Another thing to try is bladestorm followed by assault to wipe out the straglers, though this only makes sense if your safe from being charged the next turn.
I have had and exarch and 1 DA charge 3 CSM terminator and hold out for 3 assault phases and kill 1 term. I am pretty lucky with last stands though, I hagve had a fire warrior sergeant kill the last terminator stand granting enough VP to win the game
DA's are good and cheap troops and I run 3 units in most builds, as a beil-tan swordwind they are my cannon fodder, I usually finish the game with one unit in tack on around half strength and one wipped out or with only a couple models depending on if its CTF or anihilation.
DAs are Aspect Warriors and as such I believe it's good starting potential for them.
With all due respect to the other speaking "Shoot only" I believe I have a bit more experience in using CC Avengers - as I never use other configuration...
The Dire Avengers with Shimmershields, Defend ad Fortune (preferably Farseer included) may seem expensive, but those are units you buy nevertheless - just stick Farseer t othem, they gonna be great bodyguard. Now, once Fortuned, and with ttriple-wound-possesing character those guys can take anything but 30 orks on the charge. They are great block unit, greatest anvil in Eldar army for CC, far better than Wraithguard.
Countless times they have stopped charging Berserkers, Assault Terminators, Raptors, Genestealers, Avathar, Wraithlord, Harlequins, numerous Guardsmen, Bikers with Captain, Nob Bikers. Regular SM or Termies don't even have a chance to break through. I personally think that their greatest achievemnt was holding unit of Doom consisting of Terminator Librarian, 6 Assault Terminators & Vulkan He'Shtan. They simply stood. And fought back...
So, that's the anvil. Perfect for Banshees to charge in. This manuoever is easy to accomplish and devastating.
Not to mention that once or twice they tore Bersies before Banshees could reach them to bring "help".
Underestimated, incredibly tough, shooty as hell, Scoring. Maybe non-Eldarish in use, but powerful.
And besides, cool-looking Exarches included.
Oh, I bladestormed, so I cant shoot next turn, so I may aswell take Defend, and use my higher initiative to beat them! or tie them up too atleast...
When faced by an army of awesomness, RUN.
Adding Rep is always nice for everyone!
With the shimmer shield and defend they become ok at combat, with a fortune seer they become above average and a good tarpit but in the end all those points can go toward other units.
If you plan on assaulting after shooting normally, I would go for the diresword/pistol set up a bit cheaper than shimmershield and gives another powerweapon swing. The speed of eldar will generally mean they hit first and hope you can finish off the survivors.
However, truth tells, that killers are Banshees - DAs with S3 and a single PW, unsupported and most importantly, without Grenades are mediocre in assault at best, meaning they can have problems with overwhelming enemy, which often makes you waste your unit or even loose it. Additional PW attack is not even near being as useful as -1 A and 5+ inv with Fortune.
I disapprove of basically all Eldar units in CC. Banshees are specifically meant to deal with MEQS and must have Doom, but they're dead if their transport is popped. Scorpions can Outflank, but if they don't charge that turn they'll probably die as they're T3 Marines, typically in a small squad. If they Infiltrate, they can't charge Turn 1 so they give anti-infantry guns something to do.
I don't see why you wouldn't run DA's in the typical fashion, where they can already mop up. Adding those upgrades just doesn't make them a reliable CC unit, plus it's a bigger motive to blast apart their transport, which your opponent should already be doing.