I can't see a legacy option - but when one purchases blade themes, they still show up in the background of the NxE. Let's be fair: a "theme" just consisted of five separate images, one for each blade. The NxE uses the images as backgrounds.
I currently have the Castle Crashers theme (Free. I would, like you, be very hard pressed to pay for five jpgs) and it carried over to the NxE.
I highly doubt there's going to be a way to go back to the dashboard. It's defunct, and doesn't support the functionality that Xbox Live has gone forward with (Avatars, netflix, parties, etc.)
Rada: It just automatically comes when you go online with your 360.
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