Yeah, the urge to buy packs to "catch up" is strong. I'm in even worse shape than you are, in that I need a lot of legends and even rares and commons from classic, AND I've only opened a couple of GvsG packs so far. I've actually decided I'm going to buy classic packs for a bit first, trying to earn 100g per day to buy one pack per day. Even if I have to win 30 games per day to do it, lol.
My rational for not buying cards with real money is this: my need for cards gives me a reason to play. If I simply bought all the cards then my only goal would be reaching legend rank, and if I did that then I might lose interest and stop playing. So instead I'm traveling down the gradual path of improving my card collection daily and slowly.
Yeah I get what you mean on your stance of not spending money since it pretty much kills the need to play the game.That being said, I already spent $20 on Naxx, $20 on GvG packs, and had $50 worth of Amazon coins I got for free back in the day that I used on more GvG packs in the past 2-3 months that I've been playing.
I'm also missing the most basic of cards like Loot Hoarders, SI Agents, etc. I should have spent my dust crafting those but I used up most of my dust on Dr. Boom and Ragnaros since the only legs that packs have given me were Mogor, Nat Pagle and Shredder. Made a few epics as well.
I've managed to make a decent Shaman deck that gets me to around Rank 9-10. Still need cards like Sylvanas and just can't justify spending all my dust on class specific legendaries when I don't have the other cards to make a full deck. Slowly spending 100G at a time on classic packs but they keep giving me the same old junk.
Also I need to make Norzdomu for all the people who take their full turn to make a move despite it being an extremely simple decision. It's a shame it costs 9 mana to play though. Wish they "nerfed" it down to a 5-6 mana 4/4 or 5/5 card.
Norzdomu + Mogor + Sylvanas + Ysera + a bunch of taunts with divine shields sounds like a ton of fun.