Which Stuff Packs do you think are worth buying?

None.

I have all the stuff packs because I wanted more content in my game, but truthfully, I don't use them beyond trying out the new gameplay. Most of the time, I forget I bought them in the first place and the two packs I got excited for (Spooky Stuff and Romantic Garden) were letdowns for me.

If I really had to choose, I'd go with Romantic Garden for the wishing well, but my answer to this question is none of them.