It is the number of active upvoters and commentators that is a better measure of the popularity of a blog, and, as you say, in a purely financial sense, the combined stake I (weighed by the percentage they upvote) of one's upvoters is the true measure of success of one's blog. The number of followers is, however, very easy to keep track of and it does have a positive correlation to the combined stake of one's upvoters. It is, after all, the number of accounts that see your posts in their feeds. 

A new twist to this is the upcoming SMT to be used for account-based voting. We'll see how successful that will turn out. It is yet another cryptocurrency to be added to exchanges for trading and speculation. Should it prove to be a better tool for discovering quality content than STEEM and SBD, it might reach a high value.

Another thing one should take into account when chasing for whale attention is that whales are few and far between. When the success of your blog depends on only a few individuals, some of them moving on to focus on something else may have a drastic effect on you. Despite the fact that crowds can be fickle, it is safer to rely on popularity among the crowd than a handful of people. One powerful upvoter going on a holiday for a couple of weeks might put a number of full-time Steemians on a canned tuna & macaroni diet. :D