I've owned 26 "Sports Cars" over the years, and only one had a removable hardtop, a 1972 Triumph Spitfire.
I had the good fortune of finding it in January of 1975, and I couldn't pass up the great deal that I got it for.
Since gasoline was pretty expensive back then (probably around $.60 a gallon) and my daily driver got about 12mpg, I went ahead and drove the Spitfire for the rest of the winter. I really liked the "Coupe like" feeling I got from having the hardtop, and because of the way it was designed, visibility was much better than the convertible top offered.
Come spring time, I used an old "wooden" block and tackle that we had hanging in our garage, and fabricated a strap system out of some leather belts to hook up to it. The roof hung in our garage all that summer and posed no storage problems at all, but I did bump my head on it a couple of times.
I think I put the top back on it at the end of October, when I sold the car.
Not everybody has the luxury of parking there Crossfires during the winter months, and having a hard top makes winter driving a little nicer.IMO
I would think it would help prolong the life of the Canvas top not having to be out in the elements as well.
If a nice looking "hardtop" could be designed, it would give the roadster a completely different look. Not that the convertible top looks bad in any way. Just something different.