From what I understand, the original intent behind the upvote system was that people would upvote well-constructed and useful arguments or discussions, and downvote posts that didn't contribute. However, the option very quickly degenerated into a like/dislike button. Technically, the incentive to exert self-discipline is a healthier environment, but really, the much more immediate reward for voting as you please is that posts you like get popular, and posts you don't get buried. This is why the Boards have their own "meta" for what gets upvoted and downvoted, and why the popularity of posts often doesn't reflect their quality.
One of the biggest issues with this kind of system right now is that abusing it has no repercussions: whereas in League, a player loses their credibility if they abuse the report system, on here a downvote will always be a downvote. Conversely, threads very explicitly designed to generate upvotes are not only fully rewarded via upvotes, but also left to thrive completely unimpeded, which means those who make them have no reason not to do it again and again. A potential answer to this could be to enforce much stricter moderation, and have individual threads and players be excluded from this system when they turn out to be abusive, but that's a whole can of worms in itself, not just because it would risk angering a lot of players, but also because it would require far more moderator resources than are available.
Because of this, what I think needs to change is the upvote system itself: as it stands, its intent is to promote a thread's visibility among others for the quality of discussion it generates, but its effect in actuality is to function as a point system, where everyone wants to have as much of them as possible, no matter the means of attaining them. Visibility on the Boards is relative to the other threads being made alongside it, but a point system is absolute, as upvotes are registered forever, so even if popular threads that do not generate enough upvotes fall out of visibility over time, by that point the damage has already been done. Effectively, the upvote system is not only inherently prone to abuse, it's simply not an efficient manner of making threads stand out when needed.
I think the solution should be to come up with an alternative system, one that would rely on promoting thread visibility at the specific time and date of the thread being viewed by the player, relative to other threads on the main page. For example, if players each day had a limit of threads and comments they could promote to the top (let's say 3), and also had a report option for low-quality threads whose usage would be tracked and moderated, not only would they likely be more careful about the threads they'd promote, but low-effort threads and comments would also be more harshly dealt with, so the Boards as a whole could be better curated. This is perhaps not how such a system would turn out in practice, but I do think the core tenets behind it need to be applied in order for any voting system here to work.