In Seneca's case, at least, he advocated similar things (playing at being a destitute beggar every now and then) to remove fear of bad circumstances, not exactly to increase appreciation of good circumstances.

Right, this is the point of negative visualization. But the two go hand in hand just like anything else that can be framed as "yin-yang".

Something I say constantly, especially to others trying to make a decision to act, is "What's the worst thing that could possibly happen?" The thing is, you probably can't even imagine the worst thing that can possibly happen from any given decision. But by saying it out loud, you try, at least briefly. And in doing so, you often realize that "the worst thing that could possibly happen" really isn't all that bad.

I wanna ask this person on a date. What's the worst thing that could possibly happen? They say no and I feel embarrassed. It's a lot easier to do scary things if you actually think about the consequences of failure, rather than letting animal fear control you.

This, I learned from the Stoics.