ok, so i know this much that transcoding between lossy formats is a bad idea. but what if i have a really high bitrate vorbis (or mp3) file, say encoded at q7 or q8 and i convert it to a lower bitrate vorbis (or mp3) say to q3 or q4. how bad is that?

ie re-encoding between the same format.

The general oppinion (fact) here, as you know, is that transcoding gives less quality than a direct encoding from source.

Still, it is accepted than when the change in bitrate/quality is big (or when you don't expect transparency), the effects of transcoding become less noticeable.

So, in your case, I think people will agree that it is a valid decision, although you might want to hear those files after doing so, to check that there are no annoying artifacts.