Personally I would favor a Ranma/Spiderman crossover myself.  The two 
have a fair amount in common IMHO.  Hmm, Nabiki gets the chance to vacation in 
New York and see Wall street, a place she's been dreaming of for a while.  
However she's heard a lot about the crime in New York and extends the invitation 
to Akane and Ranma so that she'll have some personal protection.