Kaiser, Plenty of info only on the pros and cons of partitioning.
Never been a fan of partitioning a single drive myself. Causes more trouble than its worth, if you are worried about data recovery just get second drive, internal or external depending on your system, but a USB external drive is easiest.
A partition can speed up a drive depending on what the data is, an how you use it, but windows does a better job if left alone. (It is more likely just to extend the distance the read head has to travel between data)
Lots of info online about removing partitions. If you want to keep the 8gb you will need to work with that. Either increase the C:/ to give you enough space to copy the files across from the D:/, before then expanding the C:/ again into the remaining space.
That or just copy the files over to some secondary storage while you remove D:/ (a 32GB thumb USB drive is pretty cheap these days).
As above, you can redirect MyDocs to D:/, Clearly everything then has to be in MyDocs, which wont work if you are someone who stores all their stuff on your desktop, or programs are storing things in their own folders.