I do not have the Steam version of FO3, so I don't know about modding it one or the other vis a vis the regular version. I do have FONV from Steam, and have never had any trouble modding that.
I would say it is definitely worth buying FO3, either from Steam or just finding a dvd from Amazon or NewEgg or some other store and having it mailed to you. I see Gamestop has a download version you can buy for $19.99 too.
Amazon has the dvd version for $19.17This post has been edited by SubRosa: Sep 21 2014, 06:01 PM