I wonder if the Barnacle hunt is actually a sort of dry-run. Firstly, to check the level of interest in such a hunt (and it's high!). And secondly, to check our search-rate. Assuming we find something, the length of time it takes will give them a rough indication of how long it takes us to scan (even randomly) a given number of planets.
Which they can put to use in any future alieny search.
Which they can put to use in any future alieny search.