I think the discussion is the wrong way round. The low number of votes per contribution is a symptom, not a problem itself.
(TL;DR:) In short, we need to encourage more people to contribute actively, and as a prerequisite, we also need to encourage existing active users to vote more.
First, as Yuval Filmus points out the number of votes per question depends on the nature of the site and the kinds of questions. A site like math.SE has an enormous number of throwaway questions and one would expect low votes per questions. A site like Cstheory.SE has relatively few but well-motivated questions which spark answers that often border on new research, so one would expect a higher concentration of votes per question.
I think the issue being highlighted is that this site has a poorly functioning vote economy.
It is difficult to build up a large active user base if new contributors are not rewarded for those contributions. For better or worse, SE uses reputation as a measure of how much contributions are valued by the community.
Every person participating chooses to vote or not vote on any content. Given the penalties for negative votes, those are infrequent and can often be ignored. Therefore a non-vote on a question or answer partially means "I don't think this is useful, or it is not clear", in contrast with an upvote. Unfortunately in the SE system a non-vote also means "I don't have the time or energy to assess this contribution".
So the message that a SE site with a low number of votes per contribution gives out is: the group of regular contributors as a whole doesn't have enough time or energy for assessment of contributions. This signal is the problem, not the number of votes itself.
Let's check the hypothesis that the regular contributors individually don't have enough time or energy to assess contributions.
One somewhat robust metric is the net reputation effect of individual users. Ignoring downvotes, which are discouraged and relatively infrequent, someone who has made $a$ upvotes for answers and $q$ upvotes for questions has contributed roughly $5(q+2a)$ reputation points into the reputation economy. Now have a look at the public voting behaviour of the top users of this and similar sites. As far as I can tell, this site seem to be doing OK on this measure, for the top users.
Here is a snapshot of the top five users at some related sites. Q is the number of votes cast for questions, A is the number of votes cast for answers, V is the number of upvotes, and
~rep-in is the estimated number of reputation points injected by the user into the site, computed as $\lfloor 5(Q+2A)(V/(Q+A)) \rfloor$. (The estimate has to be used because the information on the number of upvotes for questions and upvotes for answers is not public, so this estimate assumes that the ratio for questions vs. answers remains the same for upvotes as it is overall.)
rep-out Q A V ~rep-in
168633 3878 1404 5273 33373
162504 1433 1820 3253 25365
159384 1694 4059 5626 47976
120727 1799 3961 4970 41938
107325 1550 1995 1758 13736
rep-out Q A V ~rep-in
24293 360 567 879 7083
19648 2360 3368 5560 44146 (moderator)
14239 262 372 626 4966
14032 743 1078 1505 11979
13882 525 682 1194 9343
MO 1.0: (question upvotes weigh the same as answers)
rep-out Q A V ~rep-in
16482 408 562 968 7644
15681 1042 1417 2373 18702 (moderator)
10649 714 938 1625 12738
8522 1419 1197 2462 17942 (moderator)
7225 277 327 589 4539
Cstheory.SE is a site with similar topic coverage, and arguably even more niche questions and answers, yet has a similar contribution ratio for the top users.
MathOverflow has very high contribution ratios in its current incarnation (though the 2.0 site will drop because of SE's insistence on a "questions are half as significant as answers" philosophy).
Math.SE (with those tens of thousands of homework questions) seems similar to CS.SE: the top users are busy contributing to the site, but also find some time to assess contributions of others.
Based on this sample of the top users, I don't think the user ratios at CS are necessarily a problem.
What does seem to be a problem is that the active group at CS is too small. Many of the people generating activity on the site do so by asking questions in a drive-by manner. Math.SE can cope with that because they also have a large group of active users in among the buzzing of the flies. However, at CS.SE I think a lack of active users has caused the attention economy to deflate.
I did some quick manual checks and my random sample of people in the 100-1000 reputation range seems to confirm this feeling. Recall that in a deflation-driven economy, people with some assets have an incentive to not increase what others have, because their own assets will keep increasing in value over time. The top users of an SE site presumably don't really care about reputation since they are too busy contributing content, but other contributors would rationally stand to gain from hoarding their votes, waiting for others to vote for their content while not voting for others.
To check this deflationary hypothesis, more data analysis is needed, and a weighting that takes into account different numbers of people registered as a site grows, and some analysis of changes over time.
We need to keep encouraging people to use the site actively so as to build up a large active user community. We also need to encourage users to spend a larger fraction of the 40 votes per day that they are allocated by the system, so that the economy does not go into a deflationary spiral. The latter may seem unrelated, but it actually influences the former quite strongly.
Some SE questions and answers do get a lot of attention and votes, for instance because they appear on Reddit or HN, because they are controversial, because they require less technical background, or sometimes just because they were written by someone well-known.
However, the SE system does not indicate these reasons explicitly. One simply sees that some contributions have a lot of votes, while others don't.
Since votes are the only form of signalling the system provides, if there are few upvotes on a contribution, this sends a signal that the contribution is not valued.
A new user may stop contributing if they don't feel valued.
So to build a large active user community (which is also a prerequisite for the site to move out of beta, where it has been for nearly 18 months) existing contributors need to be encouraged to vote more. We should especially nudge people who are active contributors, yet who have cast close to zero upvotes.