Elk, your decisions on what bikes to have will be based largely on what kind of riding you do. If you have lots of hills where you live then obviously you won't want to get a single speed bike, or a heavy cruiser/comfort bike. If you do mostly flat paved highway riding you wouldn't really want a mountain bike for that.
My theory is to have a modest number of fine bikes in the household that suit the various purposes well, put a lot of love into those bikes, and put great parts on them over time. Sometimes getting some fine new parts for a bike you already have and making it work can be thrilling and feeling like you have a whole new bike.