Of course it's also exciting because I think exploration of low-gravity bodies will give us more information about life elsewhere in the universe than we expect it to. While reasoning about extraterrestrial life invariably means making assumptions we don't even know we're making, based on what we know about the evolution of life on Earth and the number of planets in the rest of the universe, the development of some kind of replicators outside the solar system seems overwhelmingly likely. If we think at least partly self-reproducing probes are possible - and notice above that investors right here on 2013 Earth are trying to convince people they are - then we might be better off trying to get information about extraterrestrial life from artifacts already here in the solar system than from signals.
It is also likely that lower gravity bodies are better for any entity that wants to continue spreading, since gravity wells are energetically expensive to get in and out of. If you can get matter without descending onto a high gravity surface, you should. (Yes, "but what if aliens have antigravity" - but if we're going to bother thinking about it, we have to make guesses with what we know now. Otherwise maybe they'll ride unicorns. More seriously, if they don't care about gravity, why would they waste time with small gravity bodies like Earth? Mine the cores of gas giants. Hide just outside event horizons to evade detection.)
I've given previously in detail my arguments for why these artifacts might already be here, and where we might look. Comets and asteroids was the answer, so of course I'm excited that these mining probes may explore a number of asteroids during my lifetime. If there's something obvious, excellent (and frightening).
If they don't find anything it could mean:
1. There's really nothing there to find. Intelligent life is much rarer than we think. Replicator chemistry is either not as inevitable as it seems, or there's a Great Filter between algae and interstellar expansion, or life is just rare enough that we're isolated.
2. Something is there to find, but we don't notice it at first.
Because we're looking for something alien - something completely outside our experience - it's hard to say what a gas chromatograph of chewed-up alien von Neumann probe chemistry would look like. (This is why I hope full rocks are towed back, so we can have people in Earth orbit doing real chemistry on them.)
So how to distinguish 1 from 2? Keep looking, and follow up any interesting chemistry we find, "interesting" meaning any low-entropy repeating patterns, either temporally or spatially, on low-gravity bodies. I very much doubt we're going to find a metal ship crouching amidst a flying rubble pile. I do think we'll find strange chemistry that's worth looking into, at least insofar as it's relevant to the origin of life on Earth, and at least with comets that's no longer controversial. I haven't yet seen a model which examines what fraction of asteroids we would expect to be colonized by theoretical replicators, so I'm not sure at what rate I should de-weight my expectation of finding alien artifacts on asteroids, as more asteroids are mined without the merest