Yeah, every now and then they threaten to apply the post 2006 bands to all post 2001 cars. It seems to be pretty unpopular though so I don't know how likely it is.
I am pondering going for an earlier car, but there seems to be a sub £10k sweet spot for TD5 110's which makes old (like 10 years older!) cars look poor value, although they have the older and tougher/more reliable engine.