I've used Agility Lucario quite a few times back in the BW1 metagame and the main thing it has over SD is the coverage it's able to run without a general need for priority.
So have I actually, and I agree that having to run an extra coverage move is nice. The downside (and this is an utter deal breaker for me) is that you lose an assload of power. That power loss is just insane when I tested it, and even running Suicide Spiker lead Deoxys D still made it very difficult to sweep.
Whenever I used it, I would always be thinking "shit it would have been nice to have SD here" since it was an utter failure against pretty much any team that had a wall. The stupid think is, even when you run Crunch, Jellicent still beats you!, so you cannot really argue that "with coverage I avoid the problem that the SD set has in always having issues getting around things" since the power loss means you now lose to stuff the Swords Dance set would beat. Swords Dance, for example, can just Crunch its way past Jellicent at +2, while Agility can only max out at 60% which personally, is just pathetic when Jellicent can either LO stall you, burn you with WoW, or nail you with Scald with no problems.
Last but not least there were also times when I needed something low on health, like a Latios that I could not Agility on and I really wished I had Extreme Speed, it might not have the greatest coverage, but Priority is just awesome in the game, and there was many a time where I really missed it.
I hate Agility Lucario