Reply to Headphones vs. Studio reference monitors: is it worth it for me?

Hey guys,

Thus far I have been doing all my work on a pair of Sony MDR-7506 headphones and to be honest, I have been quite happy with the results. Everything is crisp and clear, and when testing the mixes on other speakers there are no obvious EQ issues.

That being said, conventional wisdom states that mixing on headphones is a bad idea. I've done a lot of googling on the topic and, like anything really, opinions are varied. Some say you can get away with mixing on headphones, but almost everyone seems to believe that this should only ever be your 2nd option. So in light of this I'm starting to consider getting a pair of monitors.

Some things to consider:

1. I most certainly do not have a properly treated room, but it could be worse in terms of acoustic treatment as far as normal rooms go.

2. I'm only looking to spend around $400 for the pair

In light of this, the question is simple: am i likely to find anything in that price range that would give me better results than the headphones i'm currently mixing on? Or is it simply not worth spending the $?

A quick search at Ye Olde Music Shoppe reveals the following around that price range from lowest to high:
at $160 each Behringer B1030A, then KRK RP-5 G2, Yorkville Sound YSM5, Behringer B2030A, Alesis MONITOR ONE MK2 (these are actually $200 for the pair), Yamaha HS5, Behringer B1031A, and finally KRK RP-6 G2 at $230 each, thats about as high as i want to go

Does anyone have any experience with any of these they would like to comment on, good or bad? Or again, are these simply not worth spending the money on vs. my cans?