I used to be a four-finger QWERTZ typer for many, many years. (Our keyboards have Z and Y swapped as compared to US ones, so it's QWERTZ rather than QWERTY around here.) One day I got interested in ergonomic keyboard layouts and did some research. I ended up with a layout wildly different from QWERTZ called the “NEO” layout, whose purpose was to be an improvement over Dvorak primarily for German-language users.
After a little training with the help of KTouch, my typing was much faster than I had ever been able to type QWERTZ. I can't tell to what extent this was due to my sudden exposure to real 10-finger typing. Still, I learned a lot and it didn't take much time at all.
Now, the really interesting bit is that I can switch between my old 4-finger QWERTZ behaviour and the 10-finger NEO typing within a few minutes, at most. If you train the new layout properly (personally, I really needed the typing tutor software. I would have been much too sloppy just doing my normal day-to-day typing in the new layout!), I don't think you're going to lose your old typing ability, be it 2-, 4-, or 10-finger-based or whatever.
Therefore, I suggest you give it a try. It's not much work and probably harmless in every way imaginable.
Finally, there is one more thing I wanted to mention: It's not at all clear to me that 10-finger touch typing is healthier than the “jump around the keyboard” 4-finger variety that many get used to without proper training. It's certainly faster, that's true, but I seem to remember reading somewhere that touch typing is actually more strainful and consequently more harmful to your health than freely jumping around. Unfortunately, I lost the reference. Maybe I misremember, anyway.