I've done a lot of intra-euro travel on KLM as an NWA Plat, and only once was I ever upgraded. It happened on a Warsaw-AMS trip when I was on an award ticket, but I had used a rulebuster to get the seat, so perhaps that is why. However, they also upgraded my companion with me.

Now, I've been on several KLM flights where they fly with FC basically empty. They always tell me my Fare class isn't high enough to get upgraded.