There was no appreciable 2012 cap space gained by cutting Lewis (less than $10 mil, and no MLE). 2013 cap space, yes.
[Edit: now, if you'd cut Lewis, and then amnestied Blatche, that would have freed up some appreciable 2012 cap space, and been a bold and definitive alternative statement to making the deal made today. Would have been paying players a lot of money to play elsewhere, and I don't know if Wiz' management would have wanted to do that.]
In the last four years, the Wizards have finished with the 2nd worst record twice, and the 4th worst record twice.
Moving up to a bubble playoff team this coming season and instilling a new culture should help Washington develop and hopefully keep its franchise player. Otherwise, the Wiz run the risk of being the Sacramento Kings.