Thats not correct. When it was at 4.5BTC the shareprice was so high that it had a 30% annual profit. Now the shareprice again is 30% of the annual return the divs are bringing. So no, the shares werent overpriced back then. Otherwise it would mean the shares are overpriced now too.
That's a shortsighted view: back then it was obvious that ASICMINER wouldn't be able to maintain its network share indefinitely without eating the profits to reinvest. The value of a share shouldn't be linked to the short-time dividend history but take their future evolution into account (after all past dividends have zero value for someone buying shares, only future ones do).
The question today is if ASICMINER will be able to raise its future dividends. The last ones were nearly 100% mining income and 0% hardware sales. As they are on the path to gen2, if there's no accident obviously in the future they will raise hardware sales and maybe mining income too.
This is why I think it made sense to sell at 4.5 and it makes sense to buy now. Basing sell/buy decisions just on the last dividends is a recipe for losing bitcoins in my opinion.