No, you'll just earn 6 cards (1 legendary and 5 'commons').
Cards you'll earn : Haunted Creeper good for a zoo deck (it's a deck with low cost cards and very agressive)
you'll earn this if you beat Anub'Rekhan in normal.
Nerub'ar Weblord good for counter battlecry, you'll earn this if you beat Faerlina in normal.
Nerubian Egg
it'll combo with a solfurie or an Argus, because if you destroy it, you'll earn a nerubian (it's a 4/4 cards)
, you'll earn this if you beat Maexxna in normal.
Maexxna
she destroy any card she attacked, it can be usefull if you play Anduin Wrynn because he can heal Maexxna.
You'll earn this if you beat all the 3 boss in normal and you'll unlock heroic and druid and rogue class challenges.
Poison Seeds : destroy all monsters on the battlefield and give treants 2/2 for each destroyed monster.
Can combo with a druid token.
Unlock when you finish the druid class challenge.
Anub'ar Ambusher
a 5/5 for 4 mana but with a Deathrattle (Return a random friendly monster in your hand) can combo with Si 7.
Unlock when you finish the rogue class challenge.
You can find many others information on the wiki : http://hearthstone.gamepedia.com/Curse_of_Naxxramas
gaming.stackexchange.com/users/83186/Phoke
If you have the "Win 7 games in any mode" quest, Solo Adventure matches count, which includes Naxxramas.
So if you're just looking for a quick way to win against a known deck, bumrushing Maexxna with a charge deck is gonna be an easy way to get your 7 wins.
Beyond that, there is no reason to replay the wing.
gaming.stackexchange.com/users/336/Raven Dreamer
Currently, no.
Once you earn all of the rewards for the quarter, there is no point in going back and replaying them.
I would assume that at some point in the future, people will do races to see who can go through Naxxramas the fastest or something along those lines.
gaming.stackexchange.com/users/73403/FoxMcCloud
You can always try to challenge yourself with building different kinds of decks that will beat the bosses in heroic mode (or normal mode).
To start with, one deck of each class.
If you manage that, you can try imposing other limitations on yourself (only rush, only control, etc.).
That way you can make many different interesting challenges.
Your imagination is the limit.
gaming.stackexchange.com/users/50366/Hjulle
How about replaying it for fun ?
That is why we play games in the first place. 'Replay value' can mean worth generated or entertainment gained.
Single player games such as roguelikes have lots of replay value without giving any permanent advantage to the player.
Challenges: Use only basic cards.
Or only basic+common.
Etc.
( credit:Sisk )
Use your default deck.
Use random pick deck.
(probably not for hard level) Complete with every class.
Complete with only one deck.
(choose deck and class at the start) If you played Naxxramas just for the cards of course it will have no replay value.
gaming.stackexchange.com/users/2923/AnnanFay
The first playthrough of the normal mode bosses and the class challenges gives you new cards for your deck(s).And the first complete playthrough on heroic mode gives you a new card back.  But is there any reason to replay the new solo adventure after you have cleared it one time?
Is there any replay value in the Curse of Naxxramas solo adventure?
gaming.stackexchange.com
<hearthstone>
gaming.stackexchange.com/questions/178022
gaming.stackexchange.com/users/57143/Raidri supports Monica
You'll earn 6 cards. There is no reason to replay the wing. There isn't any reason to replay the Curse of Naxxramas wing.
Players stating there's no replay value to Curse of Naxxramas solo adventure.