I've had similar discussions and have come to a similar, yet different, conclusion! (now that just demands a justification)
One thing not often recognised is that STEEM never really leaves the Steem blockchain. When someone sells STEEM for fiat they transfer that amount to one of the exchangers' accounts on Steem. It is the exchanger that takes the risk of then sending you fiat in your exchanger account.
Now, it has puzzled me for some time as to why the exchangers don't actually make more money by using their STEEM holdings! Why not power up a portion and spread some upvotes? Those will also earn curation rewards on top of an exchange fees.
But they don't; not much, anyway, as far as I've seen.
So the difference between your STEEM holdings and those huge "sleeping" accounts is that yours is generating activity and rshares and spreading the value of the coin.
I think less in terms of generating value, which is subjective, and more in terms of generating activity, which can be measured mathematically - just look at the reward pool.
the reason why an upvote is worth some 21% APR compared to the +8% APR inflation rate, is precisely the lack of activity by a very large portion of STEEM holders who are either not vested or not voting much.