Personally, I think it would be foolish to cash in. He's young, decent at the level we play (and hopefully above too), I doubt is on extortionate wages, doesn't have a bad injury or disciplinary record, and could well get better with time. We may not be flushed with cash but I don't see that cashing in is necessary (at least until summer 2009 when he has a year left on his contract, and that's assuming he doesn't sign an extension).
Lomax and Black look like good prospects at full-back, but if there's one thing this season is likely to show us it's that strength in depth can make the difference between play-offs and mid-table finishes. For whatever reason you care to name (some kind of bizarre intransigence on Shez's part, lack of quality players, extortionate demands from available players, I've no idea) we don't have a great record of snapping up quality replacements in a hurry, so I'd be loathe to start selling the decent players we do have.