In principle, unless we are dying for better low light performance, shooting in more adverse weather condition, or simply has an ego issue or demand snappier frame per second, the Nikon D90 is all we will ever will need.
Having said that, in indoor scenes, it will be wise to always shoot with a speedlight. At outdoor scenes, the usual light source will usually suffice. Hence, the debate to get a more advanced body may be overshadowed by a good lens investment instead.