If I were to resteem this article, do you get any benefit from it, if so what?

Since it is past the 7-day payout window, I can't earn anymore on this post. But I may earn some followers from your resteem, which might benefit me in the future.

Also, do I get any added benefit from it (Reputation?), beyond helping my followers understand the steemit platform, of course..?

Not really.

How does a higher reputation number help, exactly?

Users might be more likely to read a post if it's written by someone with a higher reputation.

Also, if I flag you, since my reputation is higher than yours, my flag will negatively effect your reputation. However, if you flag me, my reputation is unaffected since your reputation is lower than mine.

Lastly, the higher your reputation, the more you affect others' reputation with your upvotes. For example, if we both have 100k SP and upvote a newbie, my vote is going to have more effect on their reputation than your vote because my reputation is higher.

There's a possibility that at some point in the future the protocol will be changed to have reputation play more or less of a role.