This was asked once before in ATM. A mod responded saying that doing so unnecessarily taxed the hamsters so no, don’t do it. In my search for that post, I came up snake-eyes. But I think about that post every time I ask and receive an answer in GQ.
I remember that, too. Might have been in a sticky.
So, should we observe it?
Thanking in advance in the OP is probably enough. Radio-show callers do this. If Cecil answered one of your letters back in the day you wouldn’t write him another letter to say thank you. Hopefully you closed out your original letter with a thank you.
Of course, if you have follow-up questions or need to rephrase or clarify something, I usually say, "thanks for all the responses so far . . . "
I’ve noticed this too- it used to bother me when I’d spend ages crafting a comprehensive and well thought-out reply, and be met with deafening silence.
As Cisco says, it’s just the nature of the boards, and you get used to it- but that doesn’t mean it isn’t nice to get an acknowledgement sometimes. 
I don’t so much look for a thank you as I do for a followup. Did the solution work for you or did you try something else instead. An acknowledgement is nice, but more data as to what works is even better.
Which will cover my response if I ever.
Even with the recent slow-downs, the board is not nearly as slow (for most users) as it was in the worst of times. If someone posts a well-researched or time-consuming answer, a thank you is preferable to a 20 second break for a hamster. (The hamsters always use a break to pull a drag on their cigarettes, anyway.)
I wonder if the sticky(?) was more directed to Dopers replying with an LOL, and stuff like that there, which, if there were enough of those kinds of messages, might indeed challenge the server.