Whoa, for a second I thought you said vibration before I realized you said libration.

Which libration are you talking about? Much of the libration that we experience is as a result of geometry and orbital mechanics, not necessarily movement of the Moon corporeally.

The application that I would envision for a slow hemispherical survey is to:
a) watch for out-of-plane objects that are inbound, such as comets
b) start surveying the Kuiper Belt & Oort Cloud
c) keep watching the Kuiper Belt & Oort Cloud

The main reason to keep watching the KB&OC is to look for gravitational perturbations. Once we develop a map of the orbits of the bulk of the small objects in the Solar System & Environs we can start watching for pinches and warps to lead us to unseen gravitational objects.

If a tiny black hole wanders through the neighborhood, as I've seen speculated in Scientific American (they're everwhere! they're everywhere!), then the effects will be starkly visible in the orbital records of the small bodies, much more so than in the planets or moons.

This "gravimetric" map of the Solar system will also enable such things as defining even better low-energy trajectories along the InterPlanetary Superhighways (IPS) connecting the major bodies of our system.

In fact, it's conjectured that these IPSes are a means whereby Jupiter funnels material into the inner Solar system (obviously of benefit for the building of planets, but less so for living on them). Along the same lines, it's conjectured that Comet Shoemaker-Levy 9 snuck in through the low-energy boundary at Sun-Jupiter L-2 to get at the gas giant.

It's going to take some time to assemble sufficient data to really get a handle on the situation, and that's the kind of thing you need dull, boring stable instruments for, to sit and stare at the sky for really long periods of time.

Processing that kind of data is the sort of thing that will help drive advances in computing power, perhaps even breakthroughs.

I am 100% okay with the free-space scopes getting all the attention for sexy space science like GRBs and Cepheid variable studies. It's great stuff, and orbital scopes are perfect for it.

But I am more concerned about the neighborhood watch, and the telescopes built on the Moon will be "orders of magnitude" superior to any Earth-bound telescope for mapping the small bodies of the Solar system, and watching for intruders.