I LOVE that you love Marnie! It's what I want to name DD but DH is having none of it. I think it's traditionally a NN for Marion., but would work equally well with Marina.
Your list is very similar to my list (see thread 'Name Elimination Game) so I obviously think you've got great taste in names.
A few people have said Marnie make them think of Sarnie or Mardy - I think that must be a regional or accent thing, neither is a word I would ever use of think of.
Good luck with getting your way with 'Marnie', don't think I'm going to. 