I have about 20K miles on my 10 speed ultegra commuter without issue. I've replaced the cassette once and the chain & cables every year.

This drive train has been on an '87 trek and currently '91 Trek. One was 6 speed the other 7 and neither needed any modification to fit the required 130mm rear wheel in. Depending on the bike (year, quality, and brand) it could easily be spaced at 128mm so it could fit either size.

I bought a complete ultegra 6600 triple group for $400 right when 6700 had come out. I also bought new open pros on ultegra hubs for another $200. Including the $100 for the original '87 Trek I got a full ultegra bike with the geometry and braze ons I wanted for a commuter for $700. I couldn't touch a ultegra equipped bike for that and still can't. From my experience if you want to go 9 (or 10) and know what you're doing it isn't cost prohibitive or impractical for commuting.