To me, an upgrade that clears at booking, is as valuable as the difference in price between Premium and Economy.
An upgrade that clears at the gate, and might not clear, has minimal value. This is especially true for leisure trips when I'm traveling with the family, and sitting together trumps the premium cabin.
Like you, I've found AMS to be a sweet spot in distance, connections, and clearing in advance. Sure, I might only "save" $1000 per GUC, far less than say, JNB/TLV/SYD. But a uncertain JNB/TLV/SYD isn't worth much to me.