Videomaker – Learn video production and editing, camera reviews › Forums › Technique › Editing › How to create MOV files that play full screen without distortion › Take a look at this 2011
Take a look at this 2011 Videomaker Forum exchange for a start: https://www.videomaker.com/community/forums/topic/convert-sd-to-hd-is-it-really-possible It may answer some of your questions.
Generally speaking, upres from SD to HD is unsatisfactory as there are simply not enough pixels in the SD format to permit a successful upres. At the very least you will have letter-boxing and almost certainly a softening of the PD-170 image. You might try using Handbrake to convert the SD to MP4 and see if that helps.
iMovie, like Windows Movie Maker would not be my software of choice. I suspect you’ll get more satisfactory results using Final Cut Express although I’m not a Mac user and am only guessing at this.