There's a lot of people in this game who can't theorize card combinations and come up with how new cards will properly be utilized, and need other people to come up with the ideas first before flocking to them, so something they can't understand they will just shoot down.
I remember a lot of players shot down Darkrai EX as being a bad card, when it obviously was going to be very strong. Garchomp/Altaria was hyped as one of the best decks headed into BLW-on, even though it was horrible. People thought Blastoise would be a bad deck, even though Keldeo EX could OHKO everything! Almost no one played Landorus/Lugia during states, even though it was clearly one of the best decks (with one player who did believe in it winning at least 2 states).
I think in general people are just too dismissive of certain cards. We just see it over and over again. People dismiss every card outside a few, and then pretty much every card with an interesting Ability or attack, someone somewhere finds some way to put the card into a successful deck.
The most obscure card I think I've done well with was making top cut at a states with Pinsir NXD in my CMT. It has an attack called Power Pinch, that for a Double Colorless Energy lets you flip 2 coins, and for each heads discard an Energy off of the Active. I thought it would be a good card to fit in to try to disrupt Energy for decks without Acceleration or limited Acceleration, giving my deck an extra layer of strategical depth. I think I only used it once during the tournament, but against a Vileplume/Donphan/Cobalion deck, I was in a pretty bad spot, looking to get run over pretty hard, but I looked at my hand, had DCE+Pinsir in it, reteated to Pinsir, attached DCE, rolled two dice for double heads and that completely swung the game for me.
The way I always try to look at every new set is go through, and make a list of every card that I think has a good attack or a good Ability (or almost any Ability for that matter). As far as attacks go, it doesn't always have to be universally good, but just looking for something that is able to KO Lightning weak Stage 2's, or EX's, etc. in one hit is the type of stuff I look for.