I didn't read the entire discussion, but I would like chime to in a bit.
I'm certainly not opposed to the idea of a premium service. I very much understand that there are substantial costs to the website (plus time spent developing and maintaining it of course). I was actually surprised how much the site offers for very few ads
...but the current price of the premium service is a little too high for what is offered. The features offered are just minor "quality of life" improvements, maybe with exception of the restore from backup (what a neat idea that is!). Most of these can be emulated with existing free features too (eg. the deck notes can be used as a scratchpad). None of these enable substantial new usage scenarios. When I compare this to other services, I can get Microsoft Office subscription for the same price (Personal edition) or LastPass for fifth of the price ($12 per year, offers much more substantial benefits), Wolfram Alpha Pro is slightly cheaper and even Photoshop subscription can be had only for twice the price etc. Assuming I wasn't subscribed to these, I would be much more willing to do that than subscribe to Deckbox at the current price.
Of course part of the problem is that you offer an awful lot for free, so not much remains to monetize (without alienating your userbase). I personally would be willing to pay about half of the current price for the current features (plus warm feeling I'm supporting a service I like), but I can see even that being too expensive for people. I mean, what does an average MTG player do - pay for more results per page on a service he uses maybe several times a week, or buy a Wasteland for his EDH deck?
The way I see it, there could be two levels of premium service. Cost of these basic usability improvements would be more on a microtransaction level (fore mentioned $1 per month or so) and then there would be another level with substantial improvements for traders (who, I assume would be willing to pay more).
Also the mentioned API access is a feature that could be available only to the premium users (I would happily pay for full programmatic access to my collection 
).
And on an unrelated note, one suggestion about this update: I noticed there are now two deck types "Deck ideas" and "Built decks". I would like to suggest a third type - a "Card list". This list wouldn't have a main/side/scratch section, it wouldn't be separated into card types (it should be possible to disable this separation anyways!) and would have the same filters as the collection screen (and paging and stuff). Right now I use a deck for this, but it is really clumsy (and just now I wanted to show all red cards from the list and couldn't).
Thank you for the website, best of luck!
EDIT: One more minor thing, the title screen looks a bit borked now.
