When a post is up voted (the red thumbs up)..

Should the thread be bumped?

No. Only replies bump threads. Otherwise it would be confusing and make site navigation more difficult.

Typically the only person who cares whether a post has been upvoted is the person who made the post.

Thumbs down on that idea!

eh, thumbs in the middle. maybe. i dunno.

Nah, that would make the board wonky-nuts

I think if Yoda installed a "thumbs down", many disputes would break out.

Thumbs down was an option here in the past. I've heard the old timers talk about getting a post really down voted and being bummed or pissed. I assume that's why @Yoda did away with it. Hope he doesn't mind me tagging him but only he knows the answer.

Agreed. A thread should be bumped when the conversation is being continued. A thumbs up is more like nodding when someone says something---it's a nice show of support but it doesn't move a conversation forward. You'll end up with a lot of threads at the top of the board where the last post is months (or possibly years) old and no sense of why it's been revived.

Just messing with ya

Correct. Early days, there was no up/down vote options at all, I had to write the system custom to work with the forum software (though later versions had some version of it). It was symmetrical, like reddit or (way back when) Digg. After awhile I decided it wasn't actually being used the way I'd hoped, and as such the thumbs down wasn't adding anything.

Threads get bumped for replies as notifications. Why in any world would we need to know when a post is being upvoted? How is that going to affect our lives?

it would see what people are interested in was my thought

I get where you're coming from, but I think that the problem is that any post in the thread could be the one that was liked. So you'd have no way of knowing what someone liked about a thread. (And sometimes people will thumbs up a random GIF or joke in a thread, so not even something about the original thread topic).

i could see that happening