I'm wondering the same thing, though my fixed rate goes to November 2009. My thinking so far is that the best thing to do would be to sell the house now, rent, and put as much as possible in a high interest savings account for the next 2/3 years. Your present house will be unlikely to hold its value over that time (especially as you seem to have bought in 2006), and may be worth quite a lot less. That €500 extra will no longer exist in any form IMO if you put it towards the mortgage. If you end up in negative equity you may have to give it to the bank anyhow I suppose, but I'd hang onto it for as long as possible. If you'd consider not moving, then chuck the €500 at the mortgage?
For various reasons I think I'll hang onto my house for the long term, try to buy another in 2/3 years as well, and rent out this current one. I have very little equity in this one, it's too small for the family now, but on the plus side I'm not mortgaged to the max and my repayments are a little lower than I would spend on renting a bigger place. Also, as a last resort there's plenty of room for an extension and/or I can see myself living in it again when the kids are grown up as it has a lot of good points. So I'll make do, and save as hard as possible for a deposit for the new house.
I'm a bit worried about interest rates though, so I'm considering switching to a 10-year fixed rate of 5.7%. Would that be crazy? Can I do it now with the same lender without penalties? I would obviously have higher repayments (my rate now is 4.79%) but they wouldn't be crippling and I could still save, though they would take the costs over the current rental value of the house - but where will rental values be in 2/3 years? I'd be happy just to cover the mortgage.
Sorry, OP, I hope this is relevant to your situation and I haven't hijacked your thread!