St Servaas moorings alive and well although the ANWB almanac doesn't mention them and not many people seem to choose them anymore.
Last time I visited Maastricht the free moorings in the river between the St Servaas and Wilhelmina bridges were stacked out with visitors. But judging by this recent photo their appeal seems to be dwindling, or perhaps its just a sign of the lack of boats which are out and about these days. The moorings aren't even listed in the almanac and I can't remember now whether they ever were but for sure if you are relying on that to guide you, you probably wouldn't know they were an option.
Or maybe it's the lack of facilities which makes them unpopular? It seems that 't Bassin has improved its provision for larger boats by expanding the mooring facilities to the north of the Maasboulevard bridge, accessible via the Zuid Willemsvaart and Sluis 19 route. These provide access to the stadshaven moorings for boats who can't (or don't want to) squeeze under the 3.65m off the main river at Sluis 20.