Really very little of anything folks consider 'classic Disney' was totally created by the company. It's all based on other folks stories that Walt or his corporate descendents purchased the rights to adapt to film- "Mary Poppins" is an excellent example as is "Bambi" and even "Dumbo" or "The Love Bug". Buying companies like Pixar, Lucasfilm, etc. is just an extension of this on a much bigger, more modern corporate level. Granted, you are buying fully-developed characters and properties but still- "Mary Poppins" was pretty well formed by PL Travers when it was adapted.
To me, it's much more important if the property 'fits' into the Disney brand- good story and characters- family friendly- adaptable to the company on many levels (merch. parks, etc) and I think everything so far has. It's not like Disney bought "Family Guy" or "Drawn Together" or purchased the Playboy company.
About the only thing that Disney created in film and tv that was really 'just theirs' were the classic shorts characters, the MMC and a handful of movies - "Fantasia", "Three Caballeros", "Saludos Amigos" and a few others. Frankly, Pixar, Marvel, Henson and Lucas pretty much created their characters on their own and have a better track record for being 'original', if you think about it.
Parks and travel- a whole different thing.
