TAXI.com

I am not looking for mixing or mastering plug-ins, but I am trying to improve the quality of my MIDI samples and sounds with a virtual instrument plug-in. A recurring theme on my submissions to Taxi is the poor quality of the sounds of my submissions. I am looking to add a virtual instrument library to my music set-up. I am currently using Studio One 6 and had a few questions: (1) would a virtual sound library be worth the money to spend on it? (2) what library would you recommend? (3) I am considering the Vienna Symphonic Library, Symphonic Cube, does anyone have experience with this library and is it worth the money? It is quite expensive! Let me know!
Thank you!