Tough question, as much of it depends on your own personal criteria.
Myself, I would not like to have a huge grand in an inadequate room. Id be constantly frustated at having such a wonder instrument and not being able to hear it in its full glory due to acoustics. It would be a bit like taking a Ferrari down to the supermarket, when it really belongs on the racing circuit!
Infact, I have a similar situation myself - a huge Marshall stack sitting in the corner of my studio, but not opportunity to play the thing. Its too loud for the room which means it doesnt sound good and it is difficult to play, annoys EVERYONE in the local visinity etc. I end up playing on a small practice setup instead.
So if it were me, I'd save my money, get a high quality upright, then keep the extra cash in an account for the day that I had a space to do the instrument justice. But ofcourse, only you know what is best for you.
SJ