There are quite a bit of people asking whether to spend gold or money on the Naxxramas wings. The general consensus is that using money is worth it. However, if you check out each wings' rewards, the last wing is severely lacking compared to the rest.
Every wing has at least 3 cards and a legendary, along with 2 class specific cards. The last wing only has 2 cards, a legendary and a class specific card.(Note: Kel'Thuzad seems pretty good in Control decks with many legendaries like the Warrior and Paladin versions. Check out his Hearth Head comment page for his info) In addition to that, I think the cards in the last wing are not as important as the first 4 wings as well. What is left other than for completionist, is the Naxxramas card back for defeating all Heroic Mode bosses. I personally don't find the card back attractive and liked the Ranked Mode one more.
I was initially contemplating whether to buy the bundle with money because even with 2 wings left, the bundle is still value for money, but looking at that last wing, I am now thinking of skipping the last unlock. (If you buy the bundle, you definitely have to get the last wing) The last wing can probably wait till I have amassed more cards and start to have excess gold in the future...
Update#1: Check out LiquidHearth.com's Naxxramas Cards Power Rank, Echoing Ooze, of the last wing, is in there but not highly ranked.
Update#2: With all the above said, I might still be buying the last 2 wings bundle. With the game being out so long, I find that my lack of cards is making grinding for gold even more difficult and longer as most others probably have a better deck at this point. Hopefully by the next expansion, I'll have a good pool of cards to be able to start saving gold then. If you ever want to spend money on packs, definitely use it instead on the unlock bundle and use your gold for packs instead.
