To me there's a humongous difference between 'pay for something in return (that's maybe visible to others)' and 'pay to support'. If I truly want to support something, there doesn't need to be anything in return. It's called a donation, not a subscription. "But when thou doest alms, let not thy left hand know what thy right hand doeth:", was what I grew up with, and it's still pretty deeply ingrained. I like the idea of doing the good I do as anonymously as I can. A system where you get anything in return for a payment, goes from doing something for the sake of charity, to doing something because it's perhaps the only way for you to get a certain thing.
So there's two things to discuss here:
- Paying for extra features/perks
- Ways to support SE financially
And they're two totally separate things, and they shouldn't be presented in ways where they are easily confused.
First off, paying for extra features/perks.
In addition to the points from Makoto's answer, that I agree with, I have some more thoughts. First of all, I doubt whether there'd be enough interest in a paid product to even cover the costs of setting it up. Especially when the perks you get are mainly 'invisible' (and I don't think there should be highly visible perks, more on that later). A subscription system probably regularly needs new content for which you'll likely need developers, it will probably need some marketing and branding to attract enough paying users, and there's probably also extra costs towards accountants and lawyers and such to make sure all the taxes are filed correctly and you're not selling things to countries to countries you can't be selling to.
Giving people the ability to permanently turn off ads (and tracking, though as far as I understand it, that should already be possible by just limiting yourself to strictly necessary cookies, once some issues are fixed) for a small fee at first thought sounds innocent. But I'm still not sure if this should be something paywalled to begin with, as it's very close to putting the basics of having a site that's as usable as possible behind a paywall. Even if it were, it should be clearly labelled as just another product then, and not 'sold' as a form of support.
I think a majority of users simply don't care about cookies and tracking, and even less care about ads. From the ones that do, a part will use an adblocker and block tracking without wanting to pay for this. So, I think you're left with a pretty small group that will actually want this, and will be willing to pay for it. Either because they think it's a good way to compensate some financial loss, or because they want to 'join the club' of paying users.
So, if just blocking tracking and ads may not get you enough users to warrant setting up a subscription system, then you come to the part where you have to entice users with other perks. While I half-like the idea animuson dropped in a comment about e.g. keeping the developer story behind such a paywall, I wonder if it's feasible. It's still a piece of software, it will probably require some maintenance at some point, and if there's basically no 'free-tier' for people to get to know it, it's unlikely they will start paying for a mystery product they've never gotten to use. Eventually, you'll have to come up with new (deprecated?) stuff to put behind that paywall, to make the subscription worthwhile, or interest will die out again.
While I'm slightly leaning towards the former two things perhaps being okay as a thing you could pay for, as they can be useful to users, you also mentioned a few other things, like extra association bonus or extra votes. I'd argue against those for reasons mentioned before: Functionality of the site should never be behind a paywall. Also, is someone going to get a refund if they're suspended? I'd imagine quite a few messes/complaints/angry meta rants could arise from this. Like Makoto already said: Paying for something comes with expectations of entitlement.
As for the cosmetic changes, just 'no'. But that's more personal, because I really like the minimalism of SE right now: You get a name, an image, some reputation points and badges, and that's it. Focus on the content, not the user, and I really like that. Of course you could make such cosmetic perks only visible to users that opt-in to seeing them, but I wonder how many users will actually want to pay for something like it once they figure that out: Again, will it be enough to warrant the time and money spent on setting up such a subscription, and keeping it supplied with fresh content? I don't think so.
Then, supporting SE financially.
If this is the only end goal, what I'd settle for is a donation option that gives you nothing to show off with. No badges, no extra reputation, no extra votes, no profile customization options. If you truly feel that you're not supporting Stack Exchange enough by being here, by writing good content, by doing your part in the review queues, and you want to appease your conscience with money because you block tracking and ads, that's fine.
But in that case, I'd lean much more towards a donation option, probably something like Wikipedia has, but without the big banners. I guess a small (non-blinking!) button somewhere in the sea of whitespace that's the left navigation bar or in the footer will work well enough.
Again though, setting these things up often costs money, and I don't know if the revenue made through such a button will be enough to cover it.