I dont agree. Without a decent room you cant discern, effectively, what differentiates good from not so good.
Of course you can. For example: in a bad room you have one amp hooked up and the soundstage is confined to an area around the speakers--you upgrade to a better amp and the sound becomes "bigger" and fuller. You upgrade to a better preamp and you note that the imaging is greatly improved and therefore the soundstage is better defined. The improvements you note would probably be enhanced in a tuned room, but it's not like you won't hear them even in a bad room.