The feature is very interesting.
Asking for 5$ is easily justified.
I would not pay for it, i have reached my cash-for-play threshold by Gg in-app purchases. I would love to have it free, since i passed a certain threshold of "real-money invested", as an alternative of buying the feature outright. I really mean that, suggesting to apply it to the broader player base, encouraging Gg purchases. And you get, as bonus after X$ spent, the pass-and-play feature.
As I recently suggested, the game is worth 80$ In in-app purchases approx. this might be a good marketing strategy to encourage purchases, offer this bonus, worth 5$ if bought by itself.
80$ is if you buy the 7 current factions outright by two purchases of 20,000 Gg for 40$ each. This inplies reselling the extra cards and paying for the unlockables. No relation to wins vs AI or PVP.
Back to the point of the thread, i find it reasonnable (but I'm not a Goblin) to offer the pass-and-play after 20$ or real cash invested. Some will prefer to pay 5$, some will see the 8000 Gg + p&p feature enough to decide to pay 20$.
In all cases I'm suggesting the giveaway of half a pint of beer (5$) when someone buys a round of beers to his three favourite Goblins (20$). Not much cash, that is, either way.
I would definitely use it, and I would pay $5.00 for the feature (assuming I still had money available). But some of my motivation for paying that price is to support you goblins for all you've put into the game.