Ernst, you might want to try a trial run before spending. I found the suspension much more comfortable with a 264 lb load (me & luggage) than just my ~170 lbs. Here's a thread on improving the Showa front suspension from the UK user's forum- The Cure for Jarring SDBV front forks? - Mechanical Items - The Honda NC Owners Forum.
The Tuono rear shock is a Sachs unit. here's the thread on the Tuono rear- Aprilia Tuono Rear Shock (Sachs)