Another reason why Palpatine may have developed both the droid army and the clone army is this:
Palpatine new that the droids are not as good as clones, but they are still a threat in large numbers. Also, the trade/banking/tech etc. federations are somewhat in charge at the moment, they've got the best army, and they might not like Palpatine starting a dictatorship around them. By making battle with the clones, he draws their attention away from him (because they think they are fighting the republic/jedi) and also cuts their army down to a more managable size.
Old Palpatine is on the ball...
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