This is a tough call John. Jeff has it all spot on in my opinion, so not much of what I say here will differ from what he's offered. The whole name credit thing....I know you're not really concerned with that, but it can go both ways. If you release the crappy production and people hear it, they ask "where was this recorded...this sounds like @ss?!" It's all too easy for the band to say "yeah, we know, the engineer messed it up" and it gives you a bad name.
Me personally, the meeting I have before I work with a band dictates how much power I have in the project. To me, I'm a part of the band when I work with them and for them unless there is a producer present. I don't believe in recording "their record". It's their record but I have to have some say on it due to the reputation I have created for myself.
The other side of the coin here is....you never know what will break ground in the music industry next. The least favorite thing you hear may be the next big seller. It's such a horrible business these days, it almost doesn't pay to think or even care. Your best bet most times is to be a puppet on strings unless something becomes detrimental to your business.
Then again...let's take it to another level. Any band that gets a real deal...will get re-recorded in the major label contracted studio with a hired producer etc. Just about no band today will get a major deal out of one of our studio's unless we happen to nail something exactly the way a label envisioned it. Labels can tell talent when they hear it. BUT...a horrible representation of a band can ruin their chances too. Me personally? I'd rather go down in flames sounding the best I can without sounding buzzy or delayed etc. Let the label or people I shop to make that call. Our jobs as musicians should be to deliver our vision to the best of our ability without degrading the quality to where the song isn't a song any longer.
Though I can see where Ben is coming from, I have to disagree with him because of how the word "unique" has been replacing the word "great" for far too long with artistic types. Just because someone creates something weird or abstract, doesn't mean it's good...nor should it be praised just because it's artsy if it sounds like crap. Crap is crap regardless of the art.
"something some of you guys have never got" We get it Ben...what YOU don't get is...horrible material is horrible material. It's even worse when someone ruins material that is already great "for the sake of". What you have to understand is, it doesn't matter how much art you put into something. If the end result is bad, it's bad. I like to consider myself a pro and like to think I have decent skills. I'm also first and foremost, an artist. I may not be weird or abstract, but I am an artist...and when I suck and do something bad, I will admit that it sucked and will not try to get people to buy into it because "it's my art".
If something is great and different with artistic, genius flavors, I will praise it, brag about it and tell everyone I know. But just because someone throws up on a mic or decides to mic a mouse pooping or a dog scratching his bum doesn't mean it should be praised as "great". Funny, slightly demented, weird and maybe challenging, but it's only great if it morphs into something that shows talent. Every weirdo in the music business isn't great because they're weird and artsy. You need the right combination or it's just noise man.
If this band is ruining their material to the point of it making you cringe John, I would definitely talk to them and do what Jeff suggested if you have time. Do a mix in your own image just to show them what you are feeling. The worst thing you can do is allow a band to mix their own record. They usually don't have a clue what needs to be done and it's all about hearing more "them" individually.
Since there may not be anything in the back end money wise, it's even easier for you to try to get involved in this. Especially if you really believe in this band. I've been in this situation many times before. Sometimes they stick to their guns because they don't know any different. We have to teach them cause and effect in about...oh, 20 minutes worth of talking. Then you fire up your idea of what the songs should sound like and hopefully they get a clue.
I had a band like this about a year ago. They were quite good but the guitarist hid himself in so many effects, it was just over-kill. This dude used a flanger, delay, chorus, phaser and wah all in one shot. To me, that combination won't sound good no matter who plays the guitar. Add in extreme gain with a razor sharp tone, and you can imagine how bad this sounded. The whole problem was....the guitarist had a sound in mind, but was clueless as to how he should go about it.
So with some trial and error when we weren't on studio time, I worked out what he was looking for, cleaned up his tone, added the effects he was looking for in moderation and did some other cool tricks. He just needed to be taught how to listen and what would happen if you did this that this and this to the album quality. Once they have a direction (which I know you know we don't always have the time to offer) sometimes they are very receptive to what you try to add. When they know you are not trying to hurt them and literally deliver a better product while explaining the causes and effects, most times they'll welcome it with open arms. But you have to go about it just right or you'll lose them totally.
Being dirty, punky, slightly lo-fi or even analog is fine as long as it's done right. If something sounds so loaded with effects that you can't make out what's going on and it just makes the songs sound terrible in a way that could literally tarnish your name, I think you have to try and make a difference. You're a team in the studio. A guy like you who has been in this business for a long time is a Godsend. They should be blown away to have someone like you at the helm. Granted, none of us knows what the next new "in thing" will be...but if something sounds so bad it's really bothering you, you'd be doing them an injustice by ignoring it in my opinion. Good luck with this one my friend....there are no easy answers really.
-Danny