Can't speak to the soundbars, I think they look cool and sleek but prefer seperates. As for the Sonos, I'd fix your sound issues first, upgrade your sound system, and then decide. For a clean, simple look, hook a Sonos connect into one of the inputs on whatever sound system you end up with.
The Play:5 is excellent, but you'd probably want two linked for a room that large. For a bedroom, office, etc. the Play:5 is perfect. For the price of two of them, you'd be better off in the end spending the money on your overall sound system (since a decent receiver will run what a single Play:5 costs).