I would say that part of the reason why the "wealth" experienced is after the fact is a testament to the mind's eye and the experience of subjectivity.  One of Wordsworth's critical elements in this particular poem is the idea of being able to foster a deeper sense of appreciation of the subjective experience over time.  The idea of rumination upon the expression of the individual experience is of vital importance for Wordsworth.  It is the reason why those moments where human beings are able to "see into the life of things" help define individual consciousness and allow a sense of connection to our own past that can transform present time into a portal of what was once.