I think it's too much as a FN, but I don't see any problems with using it as a middle name. Go for it!
And as for spellings, I far prefer
Casper to
Caspar (which I pronounce differently). Have you considered
Kasper ?
Monsters are real, and ghost are real too. They live inside us, and sometimes, they win
- Stephen King
PNL: http://www.behindthename.com/pnl/45898
Top rated: Isolde and Henry
Bottom: Story and Amandus