There is a difference between personal curation and a curation service.
I try diversify my upvotes with my personal account to distribute them among a larger group of users. I mostly use the communities feed for that because that are the posts I'm mostly interested in.
But when my VP is high I often fall back to upvoting people on my following feed. And then it will be mostly the same group of users that frequently makes quality posts.

But when you run a curation service you need to diversify your votes.
With our @topcomment curation service I've set up scripts to find quality posts and also allow people to nominate comments their selves.

PeakD Analytics (https://peakd.com/me/analytics) has an overview of both your incoming and outgoing votes. This can be interesting to check every now and then.