IIRC, Estrada was decent as a reliever last season. I do agree that they planned on using Happ as trade bait all along since they had SP depth. However, I like Estrada/Saunders plus extra $$ over Happ/Cabrera, but we'll see how it turns out.
Regarding Lind, you could always come up with scenarios in your head where he would've gotten you more than Estrada, but the fact is that if another team wanted him badly enough, it could've just beat the Brewers' offer. Who knows really, but I like the overall look of the team as it has a better balance between run production and run prevention.