...it begins to interact more directly with other existing systems, and therefore acquires all the value of those systems.
In the mid 1980s I was associated with a pioneering online community called the Well. You dialed the Well's special modem, and once logged on you could chat, post, and email anyone you wanted--within the Well. All 2,000 members. Within a short time after start-up the Well made a big jump and opened its mail service to the then-obscure internet. The value of the Well suddenly skyrocketed in the view of its 2,000 or so members because now they could email thousands of academic professors or corporate nerds. A few years later, the Well further opened up its system to a capability called ftp, which allowed Well users to grab files on other internet servers and allowed others to grab files on the Well server. Again, the value of the Well exploded; with only a small effort it gained the tremendous value of the entire ftp network. Eventually the Well opened up even further, allowing users to join the conversation via the web, thereby acquiring all the value of the web.
There was a cost in each step. With every inclusion there was less control of the environment, more noise, more danger of disruption by accident or hacker, and more worry that the business model would collapse. At the same time it was obvious that a totally closed Well would have died.
The idea of plentitude is to create something that has as many systems and standards flowing through it as possible. The more networks a thing touches, the more valuable it becomes.