The Thanos bump shouldn't be shocking. It's the same thing as the WD 19 bump after Michonne appeared on the season finale. People were excited to see Thanos, and are buying while the excitement is there.
Plus, all the speculators are fighting each other for the books in the rush to get Thanos inventory.
I anticipated a minor bump, not a near 1000% to 2000% increase in the value of the first appearance. Particularly when we all know that it is going to be a long time before the new Avengers film (at least 3 years if not more). I guess I anticipate that we would see a price jump of about four times tops not 10 to 20 times. Although I guess when compared to Thief of Thieves the sky is the limit. The other thing is that it is rare that there are only a handful of films that have caued individual comics' value to go wild with speculator driven purchases. I don't know, after Thief of Thieves - all bets are off for me. I can't claim to be able to predict with any level of certainty the consequences of speculator driven price jumps anymore than I can predict the weather. I'm no comic shop salesman and I'm no weather man.
Whats to say Avengers 2 is going to be his next appearance? He could appear in cap a 2, thor 2, iron man 3 before Avengers 2.