Alright, so I made a proposal about preventing new users from voting for a few days, and nobody liked the first part of it - which was about preventing new users from voting for a few days. However, the second part - about preventing vandals and spammers from voting - did not appear to receive any opposition.
So, I'm going to build upon that with this proposal.
If more than about 20% (it does not have to be exact) of a user's article edits or forum posts are vandalism or spam, respectively, the user will not be able to vote. The edits and posts will be gauged separately from each other - so, for example, if 4 out of 6 of a user's article edits were vandalism, but the user posted on the forum 20 times but never spammed, they would still not be allowed to vote due to the article vandalism. However, a user could redeem themselves by making enough beneficial edits to have the proportion of vandalism/spam drop below roughly 20% (again, not exact). Of course, after this proportion drops below ~20%, they will have to wait a week before they can vote just so we know that they can be trusted and won't vandalize/spam again. Additionally, if a user has been banned within the last 2 weeks, they will not be allowed to vote, either.