I would make the trade... will Dickey be as good as he has been, probably not... but, it's not like he's been dog meat over the last couple of years and his peripherals keep getting better year over year..
Over the last year, he has 31 QS in 37 games (leads the majors)
He has a 2.71 ERA over the last year...with a 1.08 whip and 7.40 K's per nine... he's pitched 209 innings during that time.
Biggest worry would be the cooler weather of september.. knuckleballs tend to flatten out in cooler weather... but to say that dickey sucks, is ridiculous.
Gonzalez will probably get better, but i highly doubt you see the numbers you saw out of him last year, going forward... He had a career year in BABIP (67 points above career average). this year he is only 12 points below that career babip average.
He's striking out more and walking less. His HR/FB rate is way down, so there is the hope and expectation that will rise.. but gonzalez only has 18 home runs over the last year. Many of his homeruns in san diego were to the opposite field and my guess is, the green monster takes away more than he gives.
With Butler sitting on your bench, who I believe will have better numbers or at least equal to gonzalez from here on out, i would make this trade in a heartbeat, assuming you need pitching...