When I went FX with the D700 and later to the D800 I did not want to give up my three DX lenses either so I kept a D70 and began to build my FX lens kit for my D700 and D800. So you could possibly keep your D90 and start building your D800 FX system. See my Flickr page at http://www.flickr.com/photos/yosemitead19 for my DX and FX imaging.
"Great things are not done by impulse but by a series of small things brought together." Vincent Van Gogh