I sometimes have a phase where I answer a couple of questions. Usually because at that time I have nothing better to do and get the enjoyment that I could spare someone else the frustration of figuring out something obscure by themselves, just like a random blog post or SO answer helped me with a problem.
So I suggest to always respond with at least a little "Thanks!" or something if you found such answers helpful - it shows the other person that their contribution wasn't a waste of time and was kind of meaningful for at least one other user. Helps greatly with motivation.