Anyway, just wanted to say I have given more thoughts to a payment system, and here is what I came up with.
For the long term stability of Dominion, I think subscription is the way to go. I doubt many more expansions will come after Adventures, and even if they do, those releases will be sporadic. At best, we are looking at one promo a year. So, unless you can continue bringing in new people for years to come, you guys won't make much off charging for new expansions.
So, what I do think is that when Adventures comes out, you guys should switch to a subscription service. No matter what, keep Base Dominion free. You want to attract new customers and keeping the base set free is the way to go. After that, allow people to keep whatever expansions they already bought, and if they ever cancel the unlimited subscription, they still have those expansions. I don't think this will be that big of deal. There are enough of us on here that want to play with Adventures, so we will switch over to the subscription service just to play withe new cards.
I also suggest offering a 30-Day free trial for the subscription service. 30-Day free trials usually do wonders for sales. Personally, I don't care either way, if the only way to play Adventures was to switch over to a subscription service, I would switch over regardless of a 30-Day trial or not. However, not everyone would feel the same way as me. I also suggest offering an additional 30-Days for anyone who bought every expansion or who bought a set recently prior to the subscription switch over. This is not necessary, but a good gesture nonetheless.
As far as pricing, I think $1 is too low and $4 is too high. Dark Ages came out about 3 years ago. Over 3 years, $1 month comes out to $36, less than the cost of buying all the expansions. So, yah, I am not sure on that. However, $1 or rather .99 cents does have the benefit of being attractive to a lot of potential on the fence customers. So, maybe, you will get a lot of customers at that price point that it might be the way to go.
Regarding $4, one year comes out to $48 which is absurd. It is also half the cost of Netflix, and Dominion does not offer nearly half of what Netflix has to offer. Long story short, a lot of people will be scared away by a $4 price point.
$2 is probably the best price point. Although, as I said earlier $1 might give you a lot of customers. You can always start at $2 and lower the price if not enough people are converting. $2 comes out to $24 a year and $72 after three years. A bit more than buying all the expansions currently, but this price seems fair.
$3 is pretty close to $4, sort of like how it is in Dominion. We're looking at $36 a year or $108 after three years and that seems pretty pricey to me and probably a lot of other people.
So, long story short, $1 or $2 a month is probably the way to go. Let people keep their expansion purchases. Switch over to subscription when Adventures comes out. And, optional, but probably a good idea, offer a free trial for the unlimited expansion subscription service.