So 100 points per flight I assume?

Your option are to either pay the difference in miles you need, so if you have 600 points and need 900 you can pay for the $300, but with taxes the way they are not sure you would save much on the ticket once you pay for it all (although taxes have come down recently)

Your other option is to use the points for upgrades (always the best value) but you would have to buy a more expensive Economy ticket then you usually do.

You do have a third option and that is to travel with a different airline where your miles won't expire.
On BA for instance as long as you have some sort of activity within 3 years your miles stay alive...

Where do you usually travel to in Europe?