Brian, have a search through some posts, there's plenty of Kombi's out in the bush in near stock configuration.
Check out some of mine:
http://www.aussieveedubbers.com/forum/viewthread.php?tid=21916&page=2
When I know I'm going off road I do put on larger tyres (215/75R15's) which fit on an otherwise stock 2L kombi. This is more for ground clearance than anything else. You can get some nice chunky tyres to fit stock rims (only necessary on rear), and will get you through some though terrain.
A stock kombi will keep up with most "soft 4WD's" like all the Kia's, Daihatsu’s, Suzuki's etc. Like any off roading the driver has more to do with ability than the vehicle.
If you get adventurous, keep the kombi as light as possible and take some recovery gear (there are plenty of light compact hand operated winches around). Get out there and enjoy!
Richard