Both these statements of mine hinge on my observation that the strength of a political entity can only be determined at a time of crisis. For instance, the internal economic imbalances of the EU will always make some countries overall net-winners and some net-losers with regards to trade balances. This will inevitably lead to crises.
The USA have just as much imbalance between their states as we have between our member states, but they have one thing that we don't: Federal redistribution. If you live in Alabama and recieve social aid, get farming subsidies or are employed by the military, that is paid for by the whole, not just by Alabama. So it doesn't matter if Alabama is bleeding money in all directions.
In the EU, this is not the case.
I would thus expect an EFTA-EU to fracture or implode when the economic interests of the "big" countries are not aligned for a prolonged period of time. Nobody wants to live as a net-loser in perpetuity.
Also, the EU actually has built-in decentralization! If you look at the contracts, there is ample mention of the "subsidiarity principle" and when you take a look at the legislation, it becomes clear that they actually mean it. There is even some grumbling from the highly-centralized EU states, such as France or Poland, about the increasing significance of the sub-national organizational structures (regions).
The democracy thing could be fixed, if the will was there. Assuming, hypothetically, that things continued to go the way they have gone for the last decades, the EU actually will become progressively more democratic. After all, the EU parliament only came into the power it currently has with the Lisbon treaty.
If the political will to unite Europe dissapears, the EU will collapse like a house of cards, for all the institutions and legal frameworks it has right now can't hold it together alone.