Shakey,
perhaps I am overstating the Flemish-Dutch divide; but it is definitely there (and I rather agree with you about the reasons; the Dutch can be boisterous and often appear unintentionally rude). Antwerp and Gent are the two Belgian cities I know best, so that probably colours my view. As to the Flemish-Walloon divide, yes indeed, that's another story altogether, from what I know - though I have little first hand experience other than the looks I got the first time I spoke Dutch in the "wrong" Brussels district!

As you are married to a Flemish lady you no doubt get much more practice than I do - I only manage to keep my Dutch up through calling friends regularly for a chat. And you'll get the best of the accents; I always preferred the softer Flemish and their sometimes older word usage to the "modern is good" Dutch.

Mijne besten aan jullie beiden.