In countries with a wet and warm climate, "paper" notes tend to have an even shorter lifespan than in moderate (weather wise) areas. Or, if a country has a cash centered economy, that is another good reason for using polymer notes. And then there is the issue of security; polymer notes are difficult to counterfeit. On the other hand, it costs more to make them, and you would have to get a license from Securency (unless you plan to develop your own plastic for notes).
My comment primarily referred to the climate.

And while cash does play an important role in Euroland, most transactions are electronic and cashless these days. So the remaining issue is security. As for the current series, the ECB (back then it was the ECI) had considered using polymer notes and contacted UCB, a Belgium based chemical group, about it. (Securency is an RBA/UCB joint venture.) That was in 1996, I think. Back then there was some problem with the ink which could only be applied (and removed from) the surface, so that was - apart from the cost issues - a reason to vote against polymer. Another issue was that polymer notes might be too sticky for ATMs.
Today's polymer notes are more sophisticated, but that also applies to modern "paper" notes. You can have transparent windows, some kind of "skin" on the notes, and so on. (I'm certainly not an expert when it comes to anti-counterfeiting technology, so I rely on what I read about these things.

) My point is that if it makes sense, why not introduce polymer euro notes, but if "paper" notes serve the purpose about as well, we may as well continue using paper ...
Christian