Interesting post, Eric, as I am doing some minor modifications to a tent that I bought off ebay last year.
The idea of extra fly hem loops for guying is a good one - a nice simple mod.
I'm also reinforcing the first 25cm of the pole sleeves, as I have managed to damage the sleeve netting by being a bit heavy handed when pitching the tent whilst under midge attack last year
100mm (4") sash material works very well for this.
Other planned mods include putting a mesh panel in the inner door for added summer ventilation (closable for winter use), and I'm even considering getting some stronger alloy poles, as the ones supplied seem very thin for the size of the tent (3 man Coleman Phad 3).