I found this so inspiring, I registered just to reply.
While you clearly made this for your game at a con last weekend, hopefully these comments will not be entirely in vain.
1) I would point out that both the Doc and the Muscle have moves that reference 'Make an Earnest Plea', which, if I remember (I presume) your posts on story-games well enough, is what 'Indulge your vices' became, and so there are no rules for. You also can't really just substitute one for the other - the battlefield is really a rather bad place for a Muscle to indulge his love of hookers. ;)
2) I'm sad you didn't name the Muscle's +1 grit move 'True Grit'. But that's me.
3) Indulge your vices is awesome, but I have a problem with it. Namely, that it relies on Will to be effective, and not many characters have much reason to take high Will as opposed to other stats. And it certainly won't be all of them - and I'd want all my players indulging their vices fairly regularly.
Personally, and this is just me, I'd make it a bit more complicated.
The player decides for their character to indulge their vices, and puts forward a level of consequence. I would, to note, include personal vices as well as social ones in this. So Alma, for example, would indulge her vices both when she takes dope and when she acts overly proudly.
0: No significant consequences.
Examples: involved in a bar brawl which ends with no hard feelings and no serious injuries, sleep with a hooker without problems, etc.
1: Some inconvenience, or a chance of more serious consequences later.
Examples: lose a barter (spent, stolen, ripped off, gambled away), take 1-harm (beaten up in a bar brawl), sleep with another man's wife while he's away from camp, get an STI from a hooker, etc.
2: Moderate consequences, or a chance of very serious consequences later.
Examples: make some loud disparaging remarks about the town Gentleman while drunk, get into a fistfight with his muscle, from the show: Alma Garret going to negotiate with Hearst alone, etc.
3. Serious. Fucking. Consequences.
Examples: from the show: dragging Heart through the streets by his ear, revealing the the Gentleman that you've been sleeping with his wife, just so you don't lose an argument (due to pride, natch), etc.
The level of consequence (0-3) I'd call the excess. They then roll +excess. Treat the rest of the move the same, except I'd let them mark XP for a 10+ hit, just to provide an additional temptation to go for bigger consequences.
On the other hand, I haven't given much thought to if this'll break anything. It just brings a joy to my heart to see self-destructive behaviour in characters, and it seems fairly appropriate for the setting.