RE: Why is it important to follow and upvote small accounts? - The key to a healthy community growth.
I agree that helping build up small accounts is an important thing to focus on as well (for the higher SP accounts), because it's the minnow accounts that make up the highest percentage of Steemit users, BY FAR.
It's important to keep them interested in using Steemit, because they make up the majority of people who will advertise for and on-board new users to the platform.
That's why I make a special effort to find quality content by new users and upvote it at 100% (even though I usually upvote people that I follow at 50% to extend my voting power to include more content). But I can't do it too much or I wouldn't have any voting power left to support the middleclass followers who support me.
So, there's a balance that we need to meet, if we both want to grow our own accounts and help to grow Steemit.