I remember being inspired by alternate models, catalogs, and idea books. So even for the creative kids, it can certainly spur creativity.
As an AFOL it doesn't have top-priority to me, especially considering it can only make sets more expensive. Also, the reduced variety of pieces in current sets compared to 1980s/1990s sets makes making attractive alternate models difficult. Although the bigger sets could definitely be candidates for alternates. Alternate instructions for these could easily be made available through the internet.
Creator sets indeed are a 'special case'. The piece selection of these models is also much more diverse and the sets include less specialized pieces. The availability of instructions for a bunch of different models seems to be one of the main selling points/characteristics of Creator sets.