Those numbers (1000-2000) are not accurate for the MMS67, it was the MMS13 that was limited (to 1200, I think). The MMS67 was produced in larger numbers (no way of telling how many) and was available more widely, and is also a much nicer/improved figure (the Bale likeness is weak, though).
As far as whether or not you should swap it for the DX12, that depends in which suit you prefer. The upcoming DX12 will be the Dark Knight/Dark Knight Rises suit, the MMS67 is the Batman Begins suit. There's no denying the DX12 is an improved figure overall, though some people prefer the Begins suit.