Just for clarity and as a new Silvia owner, when you talk of back flushing the brewgroup and the solenoid, is that two separate operations or one that everyone refers to as back flushing.
Backflushing takes care of both parts. I just sometimes write things a bit more detailed than perhaps necessary.
...how long a life can you expect a Silvia to have with careful ownership (regular cleaning and backflushing).
The sky's really the limit on a well-built machine like the Silvia and many others. I would also throw using proper water quality in the mix as a way to maximize machine life. Descaling does remove limescale build-up, but until then, minerals cake onto parts like rock, and that obviously can't be good for anything.