Personally, the best reward system I've seen comes from my favorite MMOTCG, Pox Nora:
There are four dailies, two of which are, "Play two games with a deck that is/has [X]," then there's a, "Win a PvP Match" and "Play [an Unranked] Match." There's a moderate bonus for having completed all four.
Two, unique matches which relate to each other are given as "Daily Skirmishes", which can be challenging, but are usually just interesting. Each gives a fixed amount of in-game currency, and completing them both gives another one's worth. (Now, someone on another thread mentioned something about Custom Maps not having any purpose, but are being still worked on...?)
Then they introduced Heroic Achievements, which are four, fortnightly challenges, requiring the use of a certain amount of cards with specific ability types ("Deploy 2 Champions with an ability containing Loyalty or Regal Presence") or more deckbuilding ("Play a deck with at least 4 Champions with an ability containing Ally"), or equipping three champions in a match, that sort of thing. Each completion gives a sizable reward, and then completing all four gives a large amount of another, secondary, in-game currency. Some of these might get done just as you play, but they encourage learning to play in different ways, which, hypothetically, could translate to BattleForge.
There's also the addition of receiving a free card of any rarity from the first few sets upon finishing a match, but that really only works for Pox Nora...
This means that players do get something interesting to do, everyday, but it's almost entirely just a perk for coming back, and they also have a reason to try new ways of playing and have something to work, over a couple of weeks, which can be done over that time, or in super-tryhard farming mode (i.e., my life), under two hours.
So if we're in the market of... considering inspiration from other models, what other unique systems have you guys encountered?
Edit: Endlessly-farmable, in-game currency is a given. (Pox Nora is time-based, capped per match to prevent weird abuse.)