Sometimes it's just about what we
want, rather than what we need. I spent rather more that £1200 on a new BMW M3 some time back, not because I needed it but because I wanted it. I've spent money on camera gear, audio gear and so on .... and yes, computer gear, not because I
needed but because I wanted it.
So I certainly can't criticise going for a 30" because it's what you want - or rather, I could, but it'd make me a hypocrite.
So if 30" is what you want (

) go for it.
As for the original question, I think given the potential onset of OLED, if I were in your shoes and wanting to spend £1200 on a monitor, I'd hold off for a few months and see how things go unless I
had to act now. If the old 2405 had died and I needed to buy
something, it'd force my hand. If not, were it me, I'd bide my time and watch and wait. After all, if you've the money now, presumably you still will in 3 months or 5 months?
Having said that, it's
possible the exchange rate will go down the toilet and prices will go up. Or, probably more likely, they'll go down as technology improves and new models come out, That, my friend, is the gamble we all take every time we buy something hoigh-tech.