Arriving in Brussels does not settle the itinerary
Brussels is a major arrival point for flights and international rail, so it naturally appears at the start of many plans. That practical role does not make it the best base for Leuven, Mechelen, Dinant, or every Ardennes valley.
If the capital is the experience you want, give it proper time. If it is only the point of entry, compare the cost of moving on immediately with the extra check-in, luggage handling, and lost morning created by a first-night stop.
Late arrivals change the sensible answer
A late flight, an uncertain border-to-platform transfer, or heavy luggage can make a Brussels night the calmer choice. A morning arrival with a simple direct train may make an immediate onward journey easier.
Do not rely on a general travel-time claim for this decision. Check the current SNCB journey, engineering work, and last useful connection for your exact date before making a non-refundable booking.
Choose one centre for a short stay
For a one- or two-night trip, repeated hotel changes often consume the time they were meant to save. Pick the city or landscape you actually want, then use Brussels only as much as the arrival requires.
Leuven and Mechelen can often work without a car. Dinant needs a more careful return plan. The Ardennes needs the most attention to the final transfer and whether one valley can support the full stay.