If weather is reasonable in the weekends Valkenburg is overcrowded. During a sunny sunday it is no fun to walk through the Grote Straat.
Souvenirshops sell all sorts of kitch they think people want to buy. But after dinner when all daytrippers has left it is nice to sit down with a beer and enjoy.
Unique Suggestions: Try to avoid the bussiest hours from 12:00-17:00 on sunday. Take a hike on one of the many routes around Valkenburg. For instance walk down the Plenkert and at the start of the route you will find a nice fairytale like bar in the woods. You can have a drink before you walk or one if you come back. If you don´t like hiking you can always sit out the busy hours here.