Voting
Pay2FuckTheWorld could work, in the sense that people who subscribe get a monthly vote on how various changes will occur. The company breaks ties if no one option achieves a 60% majority.
So for example, the players can vote on the volcano issue. Is it:
A natural phenomenon,
Caused by a great dragon roiling around which you can fight,
A gate to the Plane of Fire,
A gate to Hell,
Caused by a great machine about to emerge,
Etc.
And the developers will take that direction and develop it that way.
Similarly, gameplay could be voted on, for example what convenience is more important for us to develop next:
Mounts, which can also be used in fighting and can fight for you when you dismount,
Vehicles, which can carry cargo slowly and be used for trade between cities to improve their production, and assaulted to stymie military activities,
Pets, which can be tamed and trained with funny tricks and sent on errands,
Gear modification, things like color and tassels and devices on shields, crests on helmets, general shape of things, all cosmetic,
Etc.
The people who are willing to put their money into the game get a say. The people who don't have anything material invested in the game must make do with forum posts and meandering bitch-fests on party chat like they do now.
The choices available would not be write-in, it would be the choices the devs offer. They should have a text input linked to each account ID that you can offer suggestions freeform, and the devs can look through those and see which ones are most popular and eliminate the ones that aren't feasible.
In all cases spamming can't happen because in order to get 10 votes or make 10 suggestion-votes you would have to pay for 10 accounts. Without additional reasons to have multiple accounts, I doubt anyone would do this. And if they did, doesn't that suggest they have a serious investment in the game and perhaps you should listen to this person a little more? Finally, while "buying votes" seems repulsive in a democracy, this is more like having patrons who support and guide your work. If a patron emerges who pays for 100 accounts every month, paying attention to what he says is a good thing. And besides, you probably have thousands of accounts so while his impact will be noticeable it won't mean on player decides how things will go. And who would spend $1000 per month just to troll people?
Character Slots
I believe it's fine for a game to say that a paying account gets maybe 20 character slots but a free account gets just two. If you have alt-itis, you might wanna pay some dough. Everyone still has full access to everything in the game, but paying players can roll up a bunch of different characters to try a lot of different things without deleting old ones all the time.
There are other benefits you can give, like a boost to XP gain or loot drop rate, that seem invisible but people will totally pay for them. However freeloaders will also totally bitch about them. I think it's also fine for paying players to receive benefits in-game as long as they're a gradient, meaning free players have access to it but the paying players enjoy it more. Rather than "six mounts are free, another twelve are for subscribers" I would suggest "free players' mounts have 1x run speed, while subscribers' mounts have 1.2x run speed (which slows to 1x for 3 minutes if the subscriber has attacked or healed another player)".
Soft boosts like that are very preferable to locking off content for subscribers, or any kind of queue for content, or preferring subscribers for bandwidth or login. That kind of stuff a lot more people will complain about.