Do you get a units bonus for scanning and uploading all the data about a planet?
There is definitely a bonus for scanning all animals on a planet. You get a checklist, typically 5-10 different animals with ????. If you scan all of them you can then upload the 100% completed progress bar and get a bonus of about 200,000 credits (25,000 per animal) on top of the basic per-animal credits.
I've found no other bonuses for scanning things other than the basic per-discovery credits. It may not even be possible to upload "all data"; there seem to be a large or infinite number of landmarks on every planet, for instance.
You get bonus nanites (50 per unique species) for uploading a completed planet.