Howard doesn't give up "muffins", seems like you are just going by some "advanced stat" and not even watching him play! Also late 2nd round picks do not hold anywhere close to the value that HF puts on them. These get traded all the time, because GMs know, there is a great chance you get at best a bottom tier player and many times you get nothing out of it. If you are a going for it now team, adding a UFA that you have no intention of bringing back, is not that big of a deal, if it means you give your team a better chance to win. Howard has been phenomenal this year, and his stats don't even show how good he has played. Detroit would be dead last by a country mile if for example we had to have Bernier play for us, or if Howard was performing like Smith has for you guys. Also, our defence is bottom 1-3 in the league, and Howard has performed amazing in front of it. With the Flames he would have a much better support for him, both offensively and defensively.
I honestly believe he is more than good enough to get you into a more competitive state, as you don't need the absolute best goalie in the league, but Howard, when healthy has been a Top 10 goalie for most of the past 4 seasons.
Regarding Miller, what makes him so great? He used to be a good goalie, but now he is a backup goalie, Howard is still a starter and much better. Look how good the Blues benefited from Miller a few years ago, didn't work out so well. He has only played 38 games the past 2 seasons combined.