Agreed . To the OP. Unless you have been in Tokyo before - or there is something in Kamakura you absolutely positively want to/have to see - I would spend my 48 hours in Tokyo.

BTW - is there any particular reason you chose the Westin Ebisu? I was there (Ebisu) for the first time on this - my second trip to Tokyo - for lunch - and found it somewhat out of the way in terms of the sightseeing I've enjoyed. If you think of a big clock - Ebisu is about 8-9 on the dial - and a place like Asakusa is about 2 on the dial. Ginza/Tsukiji is about 3 on the dial.

Also - what time of year will you be going? I think the Imperial Palace area is great during cherry blossom season. Otherwise only worth a quick walk through.

FWIW - we spent about 2 hours in the Edo Museum (about 3 on the clock). Didn't see it all. Our legs/feet gave out. Robyn