[Plugin: HTML Import 2] How much clean up required before importing?

I’m cleaning up some html from 1995 for importing into WordPress. I’ve been using HTML 4.01 Strict, but is that sufficient or should I be cleaning up to meet one of the xhtml standards? (I got spooked when I noticed that the user guide lists the allowed img tag formats using xhtml syntax.)

http://ww.wp.xz.cn/extend/plugins/import-html-pages/