I always find it strange when there is a relatively simple question that quickly receives an answer, but no up vote. If a question is interesting enough to answer most of the time I think it would be worth an up vote.
I can think of cases where this might not be, but I would think it would be more rare. But it seems to be really common.
I often find that google brings me to other stack exchanges. Often to simple questions that I need help with. I always stop and up vote these since it was useful to me even if it was unlikely to be intriguing to the experts. I probably up vote 5-10 simple questions about LaTeX every week for this reason.
So, I think there is real value in having simple questions too, if they are clearly stated, not repeated a million times and clearly answered.
When I write an answer I hope to be what people will find when they search for that question. I want my answer to be the helpful one that makes someone's study session or project easier.
So, I nearly always up vote questions that I answer.
But I'm starting to think I may be doing something wrong since few people seem to do the same.