Could one become a successful researcher by writing some really good papers while being outside academia? Would it still be possible today to go from relatively unknown to a respected figure in physics by writing some spectacular papers being outside the academia? 
(Just like Einstein did)
My impression is that the likelihood of this is proportional to how theoretical the field that you have in mind is. In math or theoretical physics, it's at least imaginable for an outsider to produce an important new discovery. In High Energy Physics the idea alone seems outlandish.

That said, even in math the ratio of cranks (deluded amateurs who are convinced they have made an important discovery without having actually done so) to actual amateur geniuses is almost infinite to one. If you want to do research, in any field, the winning strategy is to study under a respected member of the community and learn how to produce, evaluate, and communicate your ideas in this way.