I have plenty of time, only thing I'm trying to avoid is actually moving around too much (the munchkin might fall asleep and I'll have to haul her, her luggage and my own) and spending too much money. 19Euros is quite a bit (it all adds up!), bus doesn't sound so bad to me.
Have been to Brussels a few times, but it's been a while. Am picking up my kid from school in London that day, making sure she's fed and then heading over to Brussels with our onigiri and sandwiches - it really isn't an opportunity for sightseeing.