I do think it is important to downvote outright low quality questions (and answers for that matter) and questions that are off topic, and I really make good use of this. I think 99% of all woocomerce downvotes comes from me.
OK, I tend to not downvote borderline (grey area) questions or very well written questions. These are normally questions that can be salvaged with a little bit of editing and also actually has more to do with Wordpress itself that the actual plugin.
As @kaiser already explained, almost all woocommerce questions are very low quality, sometime simple one or two liners, and almost all is do-my-job-for-me type of questions. These type of questions are blatantly off topic, and not just because they are all about woocommerce, but they just doesn't show any type of research or effort, neither does the OP take his/her time to construct a proper question according to the help and ask sections of the site's help. Also, these questions are too broad to answer successfully.
If we could get paid to answer these types of questions, we would be earning big bucks, as these are quite intensive worksorders that requires a lot of manhours, lol.
There is actually a new question posted by a user. This is that specific user's 7th question. I have already explained once before that woocommerce and third party plugins and themes are off topic, and still that user come back and ask these off topic questions.
This brings me to returning users. I've realized that almost all returning users that ask woocommerce questions come back at some stage and ask woocommerce related questions again (and for that matter, any questions regarding other plugins). I have not came across anyone that returns later as a beneficial member of this site.
So, to answer this, yes, we should downvote. It is beneficial to the site. Up until now, this site has been kept very constructive and beneficial to the stackexchange community, and we should keep it this way.
Downvotes helps to keep the site clean. The system automatically removes downvoted questions on cleanup if it does not have any constructive (upvoted or accepted) answers. This way, we ensure that these questions get deleted when their status goes to "closed"
Some users simply just don't worry about continuously asking low quality or off topic questions. By continuous downvoting of these questions, the system will eventually punish that user. Their account will be locked for a week. Continuous behavior of this kind will lead to an account being banned. If you really think about that, and I know it is a bit harsch, but does this community really need non constructive members.
To conclude. It is all up to you if you want to downvote or not, and no one forces you to do that. I hope this has shed some light on the subject