I was discussing this with @rentmoney and
@aussieninja only yesterday evening.
Packs are awesome if you like to play the lotto, and I think we all do from time to time, but if you want to build a seriously competitive deck I think it's best to buy cards individually and save the packs for another time or use.
Like you also mentioned, buying in bulk during pre-sales, and selling for a small profit to buy the individual cards you need seems like a pretty solid tactic I imagine most of the players with the most impressive collections share.
RE: My Review about Card Prices, Market, Old and New Editions and the Future of Splinterlands.