I recently bought a pair of B&O Beolab 18 active speakers, which are already in a quite high price range. The sound difference compared to my old Sony speakers is enormous, but whether it's worth the price, I'll leave that open...
My dad (61 years old) switched his entire house to Sonos at the same time and is very happy with it...
When buying a system today, I would say the answer cannot be generalized... It depends entirely on your listening habits. If you are more of a daytime radio listener, I would install Sonos today. If you connect your system to the TV and enjoy "movie nights," I would go for a mid-range 5.1 system (although stereo speakers today come very close). If you enjoy evenings with a book and good music, I would definitely opt for the higher-priced range. B&O certainly builds some of the most beautiful speakers design-wise, but you pay for that. The company Teufel from Berlin also offers a quite good price-performance ratio. There are many good manufacturers, and I dare to say you won't go wrong with most of the less well-known names...