There's certainly a lot of factors that make the 'fall' of Rome inevitable... often the same things that lent it strength.
The rise of Rome as a Great Power in the world was more or less gauranteed by the military reforms that were needed in the last century BC to control those posessions that she had already gained. However, there was no mechanism included for a general control of those armies (as opposed to personal), which led to the fall of the Republic, and the continuing inability of the Empire to put a new leader up without interference from the army (which could be a fickle way to get a new leader).
The economic side can probably not be played up too much, especialy since it is impossible to determine what caused it all. It seems likely that inflation had already started before the first round of devaluation, but since the Romans didn't understand that such a thing was really possible, they didn't keep any records of the market forces that would tell us what we wanted to know. So economically, the Empire struggled with something it could only perceive by its effect, and had no body of knowlege to study it with.
In my opinion, it was likely a long-term imbalance between the coinage (or just precious metals) being made available and the goods and services available within the Empire. New metal was coming out of the mines in Spain, some metal was leaving to the orient in return for goods from India and China, and of course there's the constant slow expansion of farming and fabricae in places like Gaul, but I have no idea how these three factors relate to one another.