Personally, I doubt he'll need to reinstall Flight Sim. The built-in scenery in FS9 isn't much to look at. The fact that you didn't see any improvement in texutre quality isn't suprising.
The one thing that you wont have a problem with is framerates. When i ditched my fx5200 for an ATI 9800 pro, the difference was incredable. The scenery didn't change much, but i jacked the anti-aliasing up all the way, and i have all but 2 sliders maxxed out.
Turn on anti-aliasing... no more jaggies...
just to show you the difference:
Without and with, respectively.