Going to the moon is helluva expensive, and there's not much science left to do there that wouldn't require a massive investment (e.g., permanent human presence) for uncertain return.
As far as it taking seven years or so to get back to the Moon, that's true only because the mission-specific plans for doing it are now going on 40 years out of date. There was a really good article about this linked off of Fark last week, IIRC. Basically, the Space Shuttle isn't up to the task of taking a lander to the Moon and back, and the Saturn V/Apollo plans are all reliant on hundreds of thousands of parts, even things like washers and bolts, that aren't manufactured any longer. So, it isn't possible to re-create the Apollo missions without tons of time and expense, but that doesn't mean we couldn't put a goodly-sized unmanned probe (or a new manned lander design) on the moon in short order, either with Titan or Energia rocket, or assembling a craft using the ISS as a staging area.
As far as alien ruins on the moon... much as the 'it all happened on the dark side of the moon' hypothesis is interesting, my lunar globe shows the location of Tranquility Base as being nicely within the area we can see from Earth. I should think that any sizeable ruins would have been noticed by even reasonably-dedicated amateur astronomers by now.
For myself, I just hope that China's successful mission re-focuses some part of our military on the importance of a presence in near-Earth space, since that seems to be the only way our society can be convinced to bother with the expenditure of effort required to pursue knowledge and discovery beyond our own little bubble.
Maybe that's what any visiting aliens are waiting for - an end to our introverted navel-gazing. Maybe you have to start doing more than looking up and saying "I wonder what's out there" before you get your subscription to the Encyclopaedia Galactica.
