If you hire java/.net/... programmers, you risk getting "click-and-play module monkeys" that aren't very skilled in writing "real" code. Not to disrespect those language nor all coders using those languages, it's just an unfortunate trend. After all, it *IS* goddamn easy to whip up a gui in .net, delphi, vb, ...
I haven't played much around with the various toolkits, they all seem a bit heavy for my taste. I've heard a lot of good about wxWidgets and especially QT from trolltech, though. If I needed a "heavy" framework, I'd probably go with either of those; MFC might be a bit lighter, but very windows bound. WTL is like a light version of MFC without any documentation, I guess I'd rather write my own wrappers than using WTL

If you're looking to resell the system, I think you should go with something portable. Not really to have it run on different platforms, but because windows-centric code has this habit of being pretty ugly, if the API isn't abstracted. The win32 API is powerful, yes, but pretty incoherent.