Thanks for the suggestion, but I would never InDesign or any other WYSIWYG editor to design my ebooks, I'm afraid! I started doing web design almost two decades ago, and got into ebooks a year or two ago, and do all my coding "by hand" -- I would never do it any other way. No offense to Adobe or any fans of ID, of course!
As I mentioned in my last follow-up, I did manage to figure out (via a tutorial on another site) how to get my SVG to be transparent, but I still just can't seem to figure out how to get the file size down. I've tried saving with all different sorts of options selected, but even still I can't get my image (that I've been using just to try to figure things out) below ~280k -- whereas the same image as a transparent PNG is a mere 18k. Speaking with others on the MobileReads forum, this seems ridiculously large, and there should be some way of getting the file size down. I'm actually thinking of looking into third-party programs (freeware, probably!) which might provide a solution, i.e. where I can create/save an SVG in Illustrator, but then run it through some other proggie just to get rid of all the "crap" and bring the file size down to something reasonable.
And my only other question (that's left over) is regarding that "Save for Web and Devices" option, of course -- I gather that's something that must have come out after CS6, though?