So this was my situation, I'm curious how you might have handled it. After getting my Realm First Heroic Rag kill some 2 years ago, I burned out and decided to give up this game I had played for so long. Fast forward to this summer and I returned. A couple months into MoP, I found myself wanting to raid casually. With my previous guild long disbanded, I looked to some casual/semi-serious guilds.
But I would have no such luck. After being denied time and time again for a few weeks for lack of heroic gear and "Ahead of the Curve" or "Cutting Edge," I finally caved and threw up an app w/ a semi-hardcore, more serious progression guild. I must've given all the right answers and asked all the right questions because I earned my roster spot and am now geared well beyond what I set out to be, but I am paying the penalty in the future to committing to more raiding time than I really want.
My other thought was to wait until the next xpac and start with a clean slate b/c no one will have any achievements at that point. What would you have done? And why have we created this artificial barrier to entry for raiding? Because honestly I have never seen so much emphasis put on achievements and top level gear.