I've also studied history (BS degree) and I seem to always been the one who usually ends up GMing in any RPG group I join. There is likely at least some degree of corelation, there.

As to whether this helped in assembling the future history of Traveller, I would say that's fairly certain. The structure of the OTU and even that of individual adventures seems to have been inspired by elements from both Roman and British imperial histories. If one assumes that the basic nature of humanity will not change drastically in the future (e.g. transhuman memes such as the technological singularity and/or humanity "ascending" to an "better" stage of existence via nanotechnology do not occur) then study of the past is an excellent source of ideas for what may happen in the future. As the old proverb goes "there is nothing new under the sun." All you have to do is update the historical event you've chosen for the effects of different (which usually means more lethal) technology. 

 

I think so. See above.

 

While our brains do tend to get less flexible as time goes on, there are ongoing experiements with delaying or even reversing this effect. For example, luminosity.com. Also, there will always be newspapers (or the electronic equivalent). If you find yourself stuck for adventure ideas, just pick a real world story about something particularly stupid that criminals actually did, then think to yourself, "Alright. What were the steps which led my PCs to this particular bit of insanity?"