Yes totally with you on the Imperial and Palace. Not familiar with the Hoshinoya.

The Imperial seems to be not so well known to the western market, but it has a real vibe to it, partly due to the location, but also the lobby where there always seems to be things going on. Great for people watching. I've had an extended stay there, as it is the hotel used by my employer for Tokyo.

The Palace is also a great option with excellent proximity to Tokyo station as well as the metro. The hotel itself is very high quality, and probably has the best selection of on-premises restaurants in Tokyo. Rooms are smaller than say the Conrad (which has usually large rooms for Tokyo) but that seems to be a function of location. The closer you get to Tokyo Station the smaller the room per $ ratio.