I disagree. Before the Netherlands even got Belgium it had already lost New Amsterdam, Brasil, Ceylon, the Virgin Islands, Tobago, Mauritius, the Cape Colony, Taiwan and British Guyana and before it Belgium broke away the Netherlands had traded away Dutch India and Dutch Malaysia and it was too late to start any colonies in Australia. I would say that at best with Belgium the Netherlands could keep Dutch Gold Coast and maybe gain most of Borneo. Maybe, very maybe it could get a bit more of Africa (like Dutch Congo, unlikely as it is).Prevent Belgium from splitting off. This means that they are in charge of a major industrial area and will give them a much larger population base to work with. Being in a much stronger position they could end in a position to capitalise on their foothold in West Africa and establish a colony in the Gold Coast.
i would say that for a larger Dutch colonial empire, look at the 17th and 18th century (maybe with an early 19th century they can keep the Cape colony and British Guayana).