While this might be more of an educated opinion since I don't have the DR100 I have to believe you're going to be stepping up in quality pretty big
when recording to the 552.
The ONLY downfall of the 552 recorder is the fact that you don't have a visual display of what the file name is.
You can push the stop button and hear SVEN (voice synth) tell you what the next file name will be and on playback you can hear it tell you what file you're listening to.
The amount of added things you can do with the 552 compared to the 302 makes it a no brainer IF money is not the concern.
I don't think there is much doubt that the 552 would swamp the DR100. That question was unfair to the cheapo DR-100.
I am planning some type of upgrade to my kit and thought about the 702t or maybe a 744t if I wanted to live outdoors for a few months. Not that there is a perfect answer, but I am deciding whether to have more mixing channels, or more recording channels. For example if I popped for a 744t, I would only have a 3 channel mixer in the 302. I can't really afford both if I go with top-o-the-line gear. So I began thinking the 552 might be a reasonable compromise: 5 channel mixer, excellent 2 channel recorder, TC in, and SVEN. I could always add something like a tascam 680 in the future if I needed more channels.
The 552 is an amazing piece of gear. I wish I owned one. The "company" I worked for has the $$$$ for such a nice item and it truly is top notch stuff. They got it for simple on-location podcasting, LOL! The setup they have sounds better than a lot of radio stations' studios.
I got one of the first 552's off the production line. I'm not saying this to brag (not sure what there would be to brag about anyway - it's just a tool), there's another reason. There was a defect in the way the rough paint was applied to the carbon fibre shell on (some) early production units. The paint rubbed off fairly easily. Sound Devices, of course, offered to fix the shells and issued an RMA. "Send it when you can."
So here's why I'm sharing this: it never went back. I couldn't bear to be without it - and the chance that I might need it while it was off getting a little makeover outweighed the need for it to look pristine - though at first glance it does.
I even use the thing as a set of preamps in the "studio" when doing voice over work for some of my clients.
I also picked up the Tomaras-brand SD extended cable (which some people advise against - use at your own risk, etc. etc.) such that I could have front-panel access to SD cards. No issues there either.