I personally agree and disagree with you on this notion.
Sure, we (shareholders and potential buyers) know at this point that Disney owns Marvel and LucasArts (as well as many other great entities). That being said, we cannot determine how much of an effect these purchases will have on the valuation of the company, hence uncertainty.
As a general statement, the market doesn't like uncertainty and usually prices things conservatively when it comes to forward thinking.
That said, I agree that the feathers in Disney#$%$ have already been identified. However, they have not been allowed time to show whether or not they are as beautiful (or more so) than we would like to think.
For the sake of offering up another applicable analogy, let's say I tell you John Doe has 3 pieces of gold in his pocket. Once we ask John to take the gold out of his pocket to show us (i.e., seeing just how profitable Lucas and Marvel will be in the long-term), we'll know if each piece is only 0.05g each or if each pice is 50g each. While we knew all along that John had gold in his pocket, we would be much more confident in John's wealth and financial aptitude (i.e., more willing to invest in a company) if we knew that he had 50g pieces.
In short, we all know Disney is going to do well over the next few years. If you feel that Lucasarts and Marvel will prove to be a fantastic investment, then Disney is a BUYBUYBUY. If you think that people are overestimating the profitability of these investment, then Disney is a SELLSELLSELL.
Paint me optimistic, but I'm on the BUYBUYBUY train. Keep in mind that this is a dividend paying stock. My personal belief is that she has a good bit more riding up to do. If we get lucky, there may even be a split on the horizon. Disney has had a split of some kind every 5-12 years since the formation of the company. Last split was 1998. Food for thought.
Disclaimer: These are my opinions. Do your own research before you invest in anything. Make informed decisions.