I may be in the minority, but to my eyes, a modern threadless stem looks so out of place on a bike with a threaded headset and the adapters looks like a kludge. I'm not for or against either type -- I have bikes with both -- but it's a matter of context.

If there's a functional reason, go for it. Function trumps aesthetics. But if you're going for looks, this "upgrade" would be a downgrade.