One idea - and realize this is just a thought:
You could attempt to run it as more of a role-playing game, and treat each character
as its own. Granted, this would require you to create a multiple personality disorder
for the duration of the game, but it could work.
For example - maybe treat the elf as sort of a scout, and send him ahead to check things
out - keep the wizard back (like a wizard would do), and keep the wizard between the
barbarian and the dwarf for protection - which is what would normally happen, I suppose.
Another idea is to just do what you've done - add more monsters and traps, and limit the
searches. I would still allow selling treasure found, otherwise you would have no reason
to search for treasure after a certain point.
You can also add higher level/tougher monsters. Check out this website - go to the monster
section - I've added a few that might help - still working on it, though - so if you like any of
them, let me know, and I'll finish them up for you so they work as they should.
the website is:
https://sites.google.com/site/thenewgamesystem/monstersrealize, of course, I've not really play-tested these in a real game, but I think they'll work okay.