A good chocolate vape is very enjoyable. Unfortunately, they're hard to find, and the bad ones taste like dirt. I mean that literally - I've vaped a lot of flavors that should be relabeled "chocolate flavored dirt." Some of them come around with enough steep time, some don't.
But a good chocolate vape tastes just like cocoa, or some variant of that.
I agree with you that chocolate is a very difficult ejuice to create. Coffee is another that vendors seem to have a hard time with.
On the Chocolate side... have you tried MBV's White Chocolate.?? After 4 weeks of steeping its really not to shabby.
Good as a mixer also. White Chocolate and Candy Cane, both properly steeped, is yummy
I have to take a break from this Orange Dream. Chainvaping for probably 12 hours now. I will break out the Spearmint and let you know how I like it. I'm sure I won't have a problem with it. I may have bad dreams tonight about tossed salads though. 
