I would think that if you try to tackle the same challenges you'd normally do on your lighter bike but with the heavier one...then yes, it would make a huge difference. If you can maintain the same speeds (particularly up hills) then you'll get a better cardio workout. And of course, the more weight you pull, the stronger you'll get...that's the point of resistance training (in all forms).

But definitely, make sure that riding the heavier bike doesn't give you an excuse to slack off.