"Are my gifts motivated by altruism or by self-interest? Are they investments or gifts? In the end, perhaps the answer does not matter." Perhaps you are right, in the end it doesn't matter. In my little opinion, that is one of the 'genuis' aspects of steem, it capitalizes / rewards both motivations. It ultimately turns either into benefit for all.
Speaking of barter, a really cool event that happens every year in my town is a ski-swap.
It's not uncommon for some uber wealthy to go on a ski vacation at our local ski resort, Schweitzer Mountain and they donate all their gear when their vacation is over.
Wow, one-time use and they donate it? It's neat to see that others have a chance to acquire some good gear and perhaps swap for what they need.