classical instruments are usually played by highly trained musicians and thus not cheap. I am not saying that non-classical can be any less pro, but usually you don't just call a classical cellist to just jam on your guitar tracks. It's not just the instrument, but what the classical performer plays, too... a guitarist might simply wing it, but a classical musician follows certain rules known generally only to classical musicians or whoever studied some classical, and they try not to throw in the music anything that is not necessary. Wide topic....

As for the other two, yeah they should be there. I really like folk and new age too, although 'new age' can mean a lot of different things....some people call rock-fusion 'new age' , which seems strange to me