I don't have a lovely aluminium housing, but folks who do indicate that ergonomics are a big factor in their decision to - as you put it - mortgage their lives away. 
Another factor is port flexibility (ie., use of extension tubes to minimise the number of ports carried to fit multiple lenses). Particularly important with reduced baggage limits.
Also, some housings (Subal and Seacam in particular) offer superb external viewfinder magnifiers which (at a cost of more than some housings) offer an unmatched view of what the lens is seeing.
I would think that pressure resistance would only be factor for a small number of very deep divers. After all, the Ike's go to 60m which to me would seem sufficient for a majority of dives I would ever contemplate.
FWIW, Ike has indicated that he is preparing extension system (for release in '06) which may provide similar functionality/flexibility to aluminium counterparts in terms of lens choices.
Finally, a good photographer behind any camera/housing will make better shots than a bad one. So technique is often the biggest impediment to image quality. Conversely, all things being equal, it may be that a marginal improvement in ergonomics/viewfinder may mean the difference between getting THE shot and not quite nailing it. If you think your technique is up to snuff and you've got the cashola, then don't feel bad about dropping it on something beautiful.