I don't weight "swimmers" like a mickey finn.
The way I define "swimmers" vs other streamers is seemingly arbitrary, but some streamers seem to do better fluttering and darting in the current with no added weight. IMO the only real way to determine which patterns take weight, which ones take sink tips, which ones take shot, etc is to experiment.
Streamers are a funny animal. The shape and materials are very important to their action. Two people can tie a dry fly pattern a completely different way, and it will fish similarly. This is not the case with streamers, where the size of a head, length of the wing, type of materials, etc can all drastically change the way the fly fishes. All you can do is see how your own ties fish with varying weights and presentations.