Hello, we will be spending some time in Belgium and will be staying in the aforementioned towns for 9 nights. In addition to seeing them, we definitely want to see Gent, for sure, but have also considered Leuven, Mechelen, Dinant, Ypres, and Namur. Would it be appropriate to visit Leuven then Mechelen together and then back to home base? What about Namur and Dinant? Also, would we be selling ourselves short in spending 2/4 days in Brussels on day trips? We would be travelling via train.
Ypres is amazing with it's war history. Worth a stop to some of the outlying historical markers.
While in Brugge, it is worth a bit of time to pop up to Ostende to see the North Sea and the beaches. The town isn't remarkable, but the beach promenade extends for miles, plus there are sand dunes and WW2 gun emplacements to see along here too. The train ride only takes about 15 min. and costs about 3 euro or so. If you are looking for chocolate, I found the chocolate stores in Ostende to be a bit cheaper than in Brugge. This is also hand-made chocolate, but I am guessing the rents is cheaper here.
You can probably combine Dinant and Namur on one trip, since you have to go through Namur to and from Dinant anyway. Dinant is extremely pretty, but it only takes an hour or two to see everything. Namur is a little run down. If you´re visiting Leuven to see the "sites", it won´t take very long. If you´re within a few years of college age, however (and the university is in session), you´ll want to spend an evening at one of the cafes on the Oude Markt. If it´s "sites only", you can probably combine it with a day in Mechelen. Other than the cathedral, I´m not sure what else Mechelen has to offer. By coicidence, I happen to be a few kilometers away from Leuven as I write this.