Should I buy an iPod touch in Canada in July or wait 'til September and buy it in Europe?
The new model (if one comes out; it's not necessarily certain that one will) will be better. Will it be 45€ better? I don't know, and that's something only you can decide. If you don't need the extra disk space, the 8 GB model should be sufficient (despite what @comradsky's answer says, the internals of the 4th-gen touches aren't any different between the size models except the internal storage space.

All in all, I have to say the same thing I always say when it comes to buying Apple products: if you need it, buy it. If you wait, there's always the possibility that they won't release a new model when you thought they would, so you buy the old model, and then they release the new model a month after you thought they would.

Also: consider looking at the refurbished store on Apple's website. There are (from time to time) fairly good deals on current- or previous-gen items.