Indeed, they are listed as 250W motors on the http://www.currietech.com
site, while the lead acid Ezip is listed as 450W. Nobody here has ever opened both a 450W and 250W motor to see if they are the same thing. The controller on my 450W Trailz Ezip has a sticker that claims 35 Amps which means it can feed 840W peak to the motor. If the ECOride controller is 35 Amp also, I'd bet the 250W and 450W are the same motor.
Other mods to these include modified motor mount plates to fit two motors. If nothing else, it is a heavy steel frame that might be good for a rear hub motor.
[EDIT] I just looked at the parts available from the curie site and they do list the ECOride controller as 15A. This is curious as they now have a Lithium battery compatible with the 35A model. So I suppose you could get the 450W motor for $108 and/or the 35A controller for $65 as power upgrades and see if the ECOride battery can handle them. The $399 lithium battery for the 35A controller seems pricey and would require a different rack, but might be an option.