In my opinion, mini sets are the best value you can have in Hearthstone for their price. It's "only" 2k gold for 4 legendaries, 2 epics, 34 rares and 32 commons (including the 2 copies), it's 2640 dusts (if you deZ everything) total for only 2k gold. In parallel 2k gold is 20 packs, you rarely have 2700 dusts worth of cards in 20 packs (minimum is 40 dust a pack, so 800 dusts total if you have the worst luck). So yes if you're omega lucky you can pull out more than 2700 dusts from 20 packs but I never relay on luck :) I hope my answer will help you decide ! GL
You are forgetting about the guaranteed Epic card in every 10th pack.