I didn't know about mIDas, but from I read, it simply changes blocks' ID's, to make them compatible with newer versions, correct? That wouldn't solve the problem of newly added ores or natural structures, as it would convert the old world "as is", without the new entities.
Yes, when I try the Ender Chests method, I'll copy the folder completly and replace it on the new world folder.
Thanks again for your time.