One rather strange thing, when you think about it, is the incredible influence that the United States Constitution has had over political structures in Latin America. None of those polities developed under similar circumstances — the Argentine Republic comes closest, and it's not very close — and none of them had similar political traditions. So its rather strange when you realize both how universal the American presidential-bicameral model has become and how durable it's proved.
It turns out that Bolivia also has a U.S.-style senate. Before the recent constitutional reform, each province enjoyed three senators. Now each one has four. Not much of a change there, unless the system for electing those senators (still undetermined) has the result of dividing the delegations from the other provinces while united the Media Luna ones, or vice versa. That's remotely possible: the old system worked like Argentina, giving the election winner two senators and the runner-up one, while the new system is proportional. Depending on the election rule chosen, the effect would be to strengthen parties with overwhelming support within their province and split delegations from provinces with more divided electorates. But we'll need to see both what proportional rules is chosen (the constitution seems unclear on whether the provinces or the legislature will set the rules) in order to know the actual effect.
In short, in terms of the Bolivian legislature, the new and awfully-named “Plurinational Legislative Assembly” doesn't change much. Not only is equal representation preserved in the Senate; the new reserved “indigenous” seats in the lower house are designed to insure that the Media Luna's current representation will not change.
My opinion of the Bolivian senate, however, is very different from my opinion of the Argentine, American, and Brazilian senates. Those are undemocratic travesties that need to be reformed. (Here's a much more democratic way of apportioning the U.S. senate among the states.) Inertia and the power of special interests are the only reasons to keep them.
The Bolivian senate, on the other hand, is a necessary compromise to hold a deeply-divided country together. President Morales's original proposal for a single-house FTFP legislature with a block of reserved “indigenous” seats would most likely have served only to keep fueling the political violence that wracked Bolivia last year. Given that it's hard to see anyone benefitting from a breakup of the nation, the undemocracy of a senate is a price worth paying.