So, what I did was go back to the original MP4 bits (which I'd edited together previously in the Flip software), convert them to .WMV files, and pull those into WMM to edit. While this gave me the editing abilities that weren't in the Flip software, somewhere along the line a lot of sharpness was lost. So now I have titles and credits, and a voice-over at the end, but it looks a lot blurrier than it had previously.
I'm now wondering if I should drag in the .MP4 originals and see how WMM works with those (when I pulled in the full movie, it wouldn't even play ... I had audio but no picture). Now that I have a dedicated video camera, I'd love to go back to doing Vblog things ... and I'd like to have a "system" down where I knew I'd be able to edit things and still have them look good!
{EDIT: I did a small sample video with titles, credits, and several bits of video, pulled in as .MP4 files, and it worked fine ... I guess it didn't like my pulling in the full movie and trying to slap on the other stuff}