The advantage of a CSS solution to show icons is that you only need to declare it once, and the browser will use the style on ALL your icons. This prevent generating DOM elements which is really bad for performances (see Some thoughts on performance)
However, the more icons you want to use, the more CSS will be generated so be careful with that.
On my wiki, I generated a CSS icon for all of the core images and did not experienced significant lag so I think you should be fine.
See TiddlyTweaks — Small tweaks for TiddlyWiki (this tiddler use the old version of the filter)