Some of the vihuelists loved to use high frets all across the neck, which are much more easily accessible on the vihuela, having more of them on a narrower neck. These pieces get pretty tricky on the lute, where you can't get a full octave range without playing on the table and crunching up against the body at the neck. If you think you'd like to do a lot of the Spanish repertoire, perhaps an actual vihuela would be the best choice.
Leonard Williams PS--I don't own a vihuela, but I've tried the vihuelists on lute. To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
