To add to what Swamp Link said, if you end up wanting to buy the fourth wing of Naxx (and Mad Scientist is really great if you play Mage/Paladin/Hunter), if you end up caving and use real money, buy all five wings at once- it's less expensive to buy all five at once then to buy the first four individually.
Also stuck between deciding if I want to craft Archmage Antonidas or save up for Dr. Boom for use in Aggro Mech Mage (stealing the deck from
here . I feel the late-game cards that can come from Antonidas + a taunt or two outweigh the Boom Bots and 2 more attack, but the fact that Antonidas is such a high-priority tar makes Dr. Boom a lottle more useful. Opinions?