The only VR drops I ever got was from the Q event earlier this year (and they weren't that rare for that event), and from the 'appropriate level item' crates from the Borg RA event. I have never, in a little under a year of playing, received a VR item from a mission or NPC drop. Ever.
I haven't played a lot on Holo in about 1.5 months, but at that time, Elite Loot was bugged. I played for 5 days and got like 6 Uncommons and 1 rare total. On Advanced, I was getting that much every day. I don't know if they've fixed this or not.
I've only gotten a couple Very Rares and a handful of Rares as loot drops and I've been playing since beta. So yeah, pretty darn rare.
A handful of rare drops. Now thats strange. Ive been playing not so very long (But I leveled up my first few toons on elite) and I got more then a handful of Blue's, whole inventories full of it. (Soloing)
Team up with your friends on elite, and u get even more.
For purples, you're right. They hardly drop just like that. I think more people in team, more chance of a purple drop. (or blue drops even).