Hello & welcome to the forum. I've been running a 2010 C5 tourer for almost a year and before that a 2005 C5 Exclusive estate. You're right about the leaking steering racks, corroding tyre valves and dodgy fuseboxes, but complaints about them seem to be on the earlier cars from 2008. Certainly my vehicle has been OK on that score, although it did have a replacement DMF/clutch just prior to being sold by a main dealer. The salesman was unable to tell me the reason for the change.
I use the car to tow my caravan so I stick to the 10000 mile or one year oil & filter change routine.