Getting L/R speakers to match your center is a good idea. What center do you have? For $350, maybe a RC-62? If so, Klipsch's suggested floorstanding match is the RF-62.
Get the speakers before a new receiver, because they might be efficent enough that you don't need a new one. Klipsch speakers need half as much (or less) power to play at the same loudness as most others.
After that, I'd take a look at replacing the Bose with a regular sub & a pair of bookshelves or surrond speakers.
What receiver do you have?