Even characters are a question mark in my opinion. Easier to balance than adding a game mechanic, but if you don't choose powers carefully, the synergies with other characters can be overwhelming or underwhelming.

Cosmetics would be where I would put the stretch goals at (like upgrading the coins to metal coins (remembering to adjust the shipping cost accordingly), upgrading the player tokens, etc), or very expensive t-shirts (as those print runs can also get complicated fast), or stickers or other "simple" swag.

Disclaimer: Have not run or funded a board game Kickstarter, only heard a podcast about one (https://www.idlethumbs.net/3ma/episodes/threes-a-crowdsourci...)