Pirate Maidens is a good game, but any good game can always be made better and some of the great things I've seen in other combat card games would work well in Pirate Maidens.
Achievements are a great way to keep players interested and focused when they've cleared out all of the levels as well as giving lower level players something to work towards as they grow up.
Common achievements are -
Collect X number of various grade cards - ie/collect 20 different three star or 8 four star or 3 five star
Max the level of 5/10/20/50 different cards
Max the level of X number of cards of a certain number of stars
Upgrade X number of cards to silver
Upgrade X number of specific star cards to silver - ie/5 three star cards or 3 four star or 1 five star
Upgrade X number of cards to gold
Upgrade X number of specific cards to gold
PVP - win 5/20/50/100 brawls
Winks - wink at 10/50/100 different players
Guild achievements - win 5/10/25/50 guild wars
Rewards for different achievements would range from some winks or a fairy all the way up to four plus star level cards and Reese enhancer cards - maybe even some unique cards that are reserved exclusively for the achievements.
Daily log in bonus
Log in/daily rewards are another popular aspect of card games and the free daily rescue is a good start, but that can definitely be built upon.
Right now the big thing is cumulative log in bonuses, ie/every consecutive day you log in earns a bigger bonus, culminating with a free rare card pull.
A 15 day campaign might look like this -
Day 1/6/11 - 50/100/200 winks
Day 2/7/12 - 50/100/200 pence
Day 3/8/13 - trap/chicken leg/kraken cup
Day 4/9/14 - 1/2/3 star card
Day 5/10/15 - fairy/pixie archer/mermaid
Nothing that's going to break the bank is being given away, but players are encouraged to log in daily for their bonus. For longer campaigns the final give away could be a free rare rescue or 300 gold or a pre-chosen four or five star card or one of the Reese four/five star enhancer cards.
Right now Pirate Maidens is giving players rewards for ever X number of people who fav the Pirate Maidens Facebook page, but there's more that can be done with that.
Most card games reward players for sending out a plug for the game on Facebook and Twitter every day - something as simple as a Facebook and Twitter button that can be pressed once a day to earn free winks, say 100 winks for pressing either button or 300 winks total for pressing both.
As with the daily log in campaign, encouraging consistent and frequent daily plugging is also important, so in addition to the daily winks, plugging on one/both a certain number of days should also earn a reward, say a pixie archer every ten days, a three star Reese enhancer card every twenty days, a four star Reese at forty and a five star Reese at sixty days worth of Tweets and Facebook plugs.