It will definitely add a half hour or more of time to search for and collect boats, and I have to assume I'll lose two or three every race. That being said, dumping a heap of mini boats into the river is guaranteed to be more exciting than two or three, and if there 20 to 40 boats, surely at least 3 would always reach the finish line.
At the minimum it will be a two-man job, easy enough for one person to stand in a narrow section of the river to catch all the boats while another person heads upstream to sweep for lost boat after the winners have finished.