The 'average user' is not going to like the fact that they do not get to exert their full influence on the site, with whatever SP they have earned/bought. I think most people would be willing to accept some reasonable threshold, but if someone has to spend 4 hours a day on the site in order to exert their full influence - a lot of people will think that is a ridiculous expectation for a social media site.

If this is the goal (and i don't necessarily believe that it ought to be) there is actually a way to make sure you pick the right number.

Make the vote target a dynamic number based on the average votes cast by users with more than 0 votes (or some number based on that)

But then you have the argument that people who are able to vote on 40 posts are not necessarily doing a better job than people who are voting on 5-10. In my opinion a 'normal' user who finds 5-10 really good posts is adding more value than someone with an author list / voting bot, that auto-upvotes 40 posts per day.

This is very true. The system was actually designed so that the guy making good selections was incentivized by curation rewards, but curation rewards have been trimmed so significantly that they effectively have ceased to matter.

The pool for those rewards used to be the same size as the pool for author rewards, but its been reduced by about 80%. First the 50:50 ratio was changed to 75:25, then the reverse auction system was implemented (the 30 min penalty)... right now, if i were guessing, id say the ratio is something like 90:10 or 95:5 in favor of authors.