I've also noticed that in past kickstarters, certain in-game rewards (i.e. custom spells) seem to be frowned on. As has been mentioned, it seems they appear too similar to pre-order exclusive DLC in AAA games, which bear the weight of much internet kvetching these days.
I'm not sure how I feel about it. For me, helping to kickstart a project is an inherently communal action, and I'm doing it in order to let a project exist for everyone to enjoy. Thus the idea that I'm paying for access to something which much of the community won't have is actually counter-productive to my desires. If anything I'd rather it be like a stretch goal, where me upping my contribution means that everyone gets better stuff.
Hypothetically:
$50 - Design a room for the game with your own tombstone inside!
Sounds much more exciting to me than:
$50 - Get 3 unique character sprites only kickstarters get!
Now, the problem here is that it's probably cheaper to design a handful of unique character sprites that can then be duplicated and sent to players than it is to process and integrated dozens of room ideas from excited fans.
For me, I want getting cool and unique stuff to be a thing that happens inside the game as a natural outgrowth of the game logic; if I know I got a sprite or a spell because I paid extra money outside the game, it cheapens the experience.
Anyway, I know myself to be an oddball in this respect, so my opinion is of limited value. Just one more perspective.