This topic keeps coming up. At least it's not the old Scorps vs. Banshees thing
I play in tournaments, and I never leave home without my Dires. People are often suprised to see them in my Swordwind army. However, I've never found them to be a detriment to my final tourney standing.
They're the cheapest of the Aspects, and using either Avenger Fist or Fleet of Foot tactics, I can usually get them into position to shoot down something. In 4th Ed., they get to shoot twice and then charge into close combat, where their extra WS comes in handy.
Also, Dires need not "make back their points" if they even slow down, say, an important enemy unit. Always think about the goal of a scenario. Some units do a lot of the killing,
if they are allowed to, others seize objectives or points of terrain. My Avengers are a flexible unit that fulfills a number of roles, in a way that more expensive (and specific) Aspects or less-able Guardians cannot.