I know we're not at the forefront of technology, but using vanilla Autocad, we've got on just dandy using XREFs and little else.
For our larger industrial oil/gas projects, we do it completely in 3D. Our electrical guys just got MEP and are fully trained and up and running on it pretty fluently, now, so they say. So they should be doing 3D work with all their cable trays and what not, if everything is smooth enough for them, next time around. Our piping guys have been doing it in 3D as long as I have, as well.
I am typically the 'model manager' which, if you read the BIM hype stuff, would make me the "BIM Manager" I guess, since I'm the one that collects the models from the subs, XREF's it all in and checks for everything to be kosher.
I do it all 'by eye' to be honest, and have yet to have a construction problem. The only time we had a 'conflict' was when the contractor didn't use elevation nuts under the base plates of a pipe bridge to bring it to the proper elevation, and instead sat the base plates right on the concrete pads, which were sloped 2%... the bridge was 30' tall, so it really skewed the piping.
I mean, if your boss -wants- to shell out the extra cash for software to be your eyes for you... I guess, why not?
To be frank, though, I don't know how comfortable I would feel letting the software do it all for me. That's a big leap of trust. Considering how intimately knowledgeable I get of the project through it's design and revisions, I don't see how it would help anything.
Seeing the projects that you guys do, it almost seems like you would be doing the same I do with these projects, and be very much involved in every inch and foot of the building in every nook and cranny, knowing it very thoroughly. If you're that involved in your project, you'll probably already see conflicts and problems with clearance, before some software can even tell you.
The other issue I have is when you don't have a physical CLASH, but you still have a problem with space. How will NavisWorks know that you need to have enough room around a pipe to access the ball valve handle? What about needing to have 48" clearance in front of a switchgear cabinet? How will NavisWorks know that you need to have those special access spaces around mechanical and electrical items?