Maybe I am alone in this line of thinking. If I am, by all means tell me. But these special challenges are now just a waste of time to me.
When they first launched, they offered a 50% discount to normal challenges and the new most efficient (albeit grindy) way to farm gold. You'd be a fool to not participate; given that you could consistently get >2 wins. It also forced you into new game modes and playing new cards. Because of the value they provided, it was easy to forgive the downsides (more on that next).
Fast forward to today and the value is gone. They are the same price as normal challenges and now the downsides to these game modes are intolerable for me. The main problem is that these modes have a definite luck factor involved. Sometimes you get great cards, other times you have absolute garbage. I don't believe we have had the full price Blind Deck challenge yet; but we all know luck played a significant factor in that challenge as some decks were downright difficult to use. In these special challenges, my wins are never consistent (luck factor). I had rounds where I got 2 wins, followed by a round where I got 10 wins. Whereas in the regular challenge, I can always expect at least 8-10. And no, I don't use meta decks.
The point is, why would I use gems on a Special Challenge that has a noticeable luck factor when I can be, on average, more successful in the regular challenge that is far less reliant on luck? Some would say it's for the fun or novelty. But then, in effect, we are willingly spending gems to use a game feature as your return on investment is lower.
Now, the value argument is void when people can access new cards earlier (Ewiz, Ram). However, that raises another problem. In a recent thread by Killerkuto (sp?), he raises the concern of a rapidly shifting card level imbalance in Arena 10. Further discussion in that thread noted P2W further pushing down players in A8/A9/low A10 due to the nature of card releases. The problem is that the better players are getting early access to potentially unbalanced cards. While the underleveled or less skilled players have no chance at these cards AND are further pushed down the ladder by these players. It adds to the great divide that is currently happening. Nothing will kill a game quicker, or prompt people to retire more, than a feeling of absolute helplessness and hitting a massive brick wall.
So, for me, I've been taking my free entry and moving on. Often times doing the regular challenges in lieu of a special challenge. A couple challenges back, there was no free entry and no gem cost discount. I didn't even participate once. A definite shift from previously looking forward to these events.