As far as I can tell, the bold is not justified and not pretty. If I understand it right it's to show they're shadows, but is this important to know in the sidebar - or, rather, in tab Open where it's one of the few places shadow titles appear... other than in tab Shadow... where actually the bold also adds clutter. The $ indicates this is a shadown anyway and if you try to edit it you get a clear warning.

...

ADDENDUM, years later, after discussions that have futher clarified the problem:

The different styling is not information about the link but rather information about the tiddler. The current styling at most pre-informs you that it is a shadow (that is not overwritten) but I fail to see why this is so important to know at this stage, i.e when merely glancing the title - to do something with the tiddler you'll need to click the link. The status of "shadow or not" is really about the tiddler, not about the link.

A fair exception for link styling is missing tiddlers, so you are informed that you perhaps shouldn't click the link at all. That is information about the link, i.e what to do with the link!

The multiple native link styles bring clutter when the supposed information given from the styling is not needed or requested. (But I wouldn't mind some kind of tooltip or other opt-in to get more tiddler info.)

However, a perhaps separate issue, is that the shadow tiddlers themselves ought to clearly inform what they are, as is done e.g when clicking to edit them or when they're being edited.