I know what it feels like. That's why I hardly use MMD anymore, and why I left the community (Well, the community was getting obnoxious anyways. xD) Art Block sucks just as bad as writers block. Maybe try something new with MMD? Make videos/flash! I have no clue since I'm really not as creative as you are.
You know what, Neo? You're only feeling like that because you don't have the right "imagination" for making a picture or such. So now, move on to videos, Neo! Pictures are just one part of MMD, do videos, original motions! Stories! Themed videos! If you look trough MMD cups and such, videos aren't always dancing, it's all about free-creativity! start making videos, Neo! It will do you lots of good!
But it's not the first time it's happened to me. I mean, back when I first started using MMD on my old account, I used to do like at least a picture every day, and now, when I open MMD, I just blankly stare at my model folders.
I used to make so many pictures when I was new on dA xD Now I'm kinda lazy to make pictures /shot
Welp, It's not all about the ammount of pictures but more about the quality of them! I preffer having 1 good picture in my gallery instead of having like 10 of them that are crappy O w O don't force yourself, when you do that the ideas go awaaaaay / o /;