*SQUISH*
that is the sound I hear this list making when it comes into contact with the enemy. While you do indeed have an army of varied aspect warriors, you lack any sort of real synergy between your units.
To help you out, we'll go through some of the roles of the units being used incorrectly.
Fire Dragons in an eldar list should generally be taken as cheaply as possible in a wave serpent. The usual build is
5 Dragons
Wave Serpent-
tl shuri cannon
This comes out to 180 points. The units role is to fly into the heart of the enemy and destroy thier most important unit-such as a landraider transporting termies, etc. 5 melta guns will generally do just that. The squad should be kept cheap- because they will die . Opponents tend not to like you destroying their important models. Your squad however is on foot- they are also your only real source of reliable anti heavy tank. Add this to their short range, low toughness, and middling armor... and you've got a recipe for disaster! Fire Dragons NEED a delivery system, otherwise they will be targeted before they can get in range.
Banshees also need a transport. Your squad set up is fine, but without a transport they- like fire dragons- are mincemeat. Slow, low toughness, middling armor. If they get shot they will take massive casualties. When banshees are played they are run as a counter assault unit in a mech list. You keep them in a shooty wave serpent near your other serpents. When something scary and fast comes close- such as
fnp jump blood angels with melta guns for instance. The banshees hop out of the transport BEFORE its moved, move 6 inches, fleet, and assault. Trying to walk them up the battlefield will see them dead, and leaving them behind in cover will not make use of those power weapons. Harlequins are a better unit on foot, the shadow seer makes them relatively untargetable, they ignore terrain, get rending with kisses, have as many attacks as scorpions, and have the same strength on the charge (furious charge)
Your Dire Avengers would be ok in some lists, but not in this one. That set up requires a fortune seer, and a units which need to be protected from enemy charges- such as wraithguard. Remember, like banshees and fire dragons, are too frail to walk up the field, t3 4+ save leaves a lot to be desired.
Otherwise, Dire Avengers should take 2 catapults, bladestorm, and go in a wave serpent. That way they can deliver their impressive firepower anywhere on the battlefield.
If you do not want to put your troops in a Wave Serpent, then pretty much every other choice in the codex will outperform Dire Avengers in the troop slot. Rangers and defenders with a heavy weapon platform are better at hiding on an objective and giving long range cover shots. and Jetbikes are superior due to their t4, 3+ save, and massive movement ability- and the 3+ cover save they can claim from that.
Your warpspiders look fine. The only point of contention I have with them is that once you've taken withdraw and the powered blades, its worthwhile looking to put an Autarch in the squad.
Autarch- warp jump generator, mandiblasters, power weapon, fusion gun
An Autarch will help your Scorpions and Spiders arrive from reserve easier, and he'll add 6 power weapon attacks to anything your Warp Spiders charge, making the unit able to win combats against fire support squads.
Your Scorpions are generally fine. I would perfer the claw to the biting blade, as the claw gives you a weapon to hit units with 3+ and 2+ saves with, as well as giving consistant s6 against vehicles. Although the biting blade CAN hit vehicles harder if you are lucky.
OK
So overall you need to make some real changes. You lack the long range fire power to play defensively, harlequins make better counter charge units on foot. Fire Dragons really need a transport badly...
The only units in your list capable of engaging armor from range are the fire dragons, warp spiders and sadly your fire prisms who would rather be shooting infantry. And the Spiders cannot touch heavier armor values without an autarch with a fusion gun.
My 1500 list contains many of the units you want to include- except warp spiders... I add them in at 2000

Take a gander at it to see if its something that might suit your fancy
akaean's 1500 wrote:
HQ: 98
Farseer- Warding, Spear, Doom [98]
Elites: 497
5 Fire Dragons
Wave Serpent- tl shuri cannon
10 Banshees- exarch, executioner, acrobatic
Wave Serpent- tl eldar missile launcher, underslung cannon
Troops: 673
10 Storm Guardians + Warlock- 2 flamers, destructor
Wave Serpent- tl bright lance
10 Dire Avengers- Exarch, 2 catapults, bladestorm
Wave Sepent- tl bright lance
3 Gu Bikes + Warlock- cannon, spear, embolden
Heavy Support: 230
Fire Prism
Fire Prism
Wave Serpents are king. If you want to stay on foot... you need totally different units!