Thank you for the kind suggestions, Jeff and 57gmc.
Jeff, I just can't provide a better explanation. It would take a ton of time I don't have, yet in the end I would probably still fail to communicate.
57gmc, your post makes a lot of sense to me, though nobody who does the same work I do feels that Inventor is fluid enough to solve these issues.
Maybe a happy medium is the way to go. Using a combination of the two methods just might help you. Use XREFs during the beginning phases of a part or assembly when things are very fluid and then converting to blocks that are stored in a library as they become more solid.
I'm really grasping at straws here because you really haven't given us any idea what it is that you do. Maybe you could give us a general description of a "typical" job, if there is such a thing, from start to finish.