A drawing’s purpose in architecture is to control an idea—or to convey it to others who are involved in the realisation.
Therefore a drawing carries the official signature of the office, but a sketch used in the context of the design process does not carry a signature. Why, for example, would I sign a sketch? I know my own name; it’s redundant. The only interesting and relevant thing would be a date. A genuine original sketch never carries the name of the architect.
I would accept in principle the idea of a sketch exhibition; but only in the context of the idea’s development, or as part of the process leading to the final building. And only to show how the sketches conveyed ideas.
The beauty of a drawing is misleading. The appeal of a sketch is its transcending character; it is pointing beyond itself, a means of preparation serving for something else, a message about architecture or about a certain project or about a certain detail. Graphic arts get untrue or ridiculous if they lose their transcending aspect and are taken as final purpose.