You shouldn’t need a car unless the convention site or hotel aren’t convenient for mass transit. It’s easy to get to Ogden via UTA FrontRunner and there’s lots to see within a short distance from the Trax light rail. Maybe you can get a start here http://www.visitutah.com/travel-regions/northern-utah/salt-lake-city/ .
If you do get as far north as Ogden, you can visit Union Station. There is a fairly decent railroad museum and an incredible museum dedicated to John Browning.