I play with the normal and sport mode when travelling fast in twisties and the difference is quite noticable. I have not driven the standard suspension (mag is standard in US) so I cannot say how the stiffness compares to the norm and sport modes on magnetic, perhaps somewhere in between?
Either way I am sure its a well balance set up and doubt very much that your missing much.
I have a '08 TT 3.2 S-tronic. It does not have the mag ride, and has all-season tires instead of summer performance. I can give you a head-to-head comparison between two recent Audis, but they are somewhat dis-similar cars. This is all street driving, I haven't had either on a track, yet.
The TT has a very secure and confident, yet comfortable, ride. When you drive it agressively I do wish it had a little less body roll. The mag ride would probably help with this, although I assume more agressive tires/rims would make a big difference also.
The mag ride on the R8, as mentioned above, is always on. In either mode when the suspension deflects more rapidly, the damping increases. It's more aggressive in the sport mode.
In USA mag ride is standard, and IMHO Audi USA has it right. The mag ride is a worthwhile addition to the car.
The Mag Ride must be the source of the "flat" drive that the R8 provides. I passengered in 5 different cars for "hot laps" with driving instructors and the R8, by far, was the flattest drive. The ride was still thrilling, just without the drama.