There is a term for a showcase of temporary exhibits. An Exhibition Hall.
Nonetheless, I have not referred to the Guggenheim as such. It is in fact a museum, with a permanent collection (barely shown), exhibition space (poor for showcasing art but breathtaking none-the-less), and a curatorial team (uneven - for every good-to-great exhibit they put together, there are a dozen nondescript or bad ones). Taken together - I think its a lousy museum - whose showcase work of art is the building itself.
Should a tourist go see it? Definitely. But as a local, once I've seen the soaring space - the permanent collection gives little reason to return. Do they occasionally have a special exhibit worth seeing? Sure - and I do go on occasion. But never for the permanent collection - I've seen regional museums with much smaller collections that show their meager collections better.
Even compared to other spaces that host temporary exhibits, I think they don't do as good a job (anyone else miss the showcase where IBM would host exhibits at twice a year, in the basement of the old IBM building? That curatorial team almost always hit a home run, year in and year out) .