Wait just a minute here. Buying VSL or any other library will not make your soundtrack sound true, specially if you are unfamiliar to the library. Don't forget that a lot of people own these libraries around and still can't make them sound like the amazing demos we see in the official websites.
Unless your are really confident about your skills on mixing, arranging and programming, you should not rely the quality of your composition in any Library available at the moment. As an alternative, change the aproach of your arrangement, and make it sound smaller, but with real musicians. It will surely sound more "natural" this way.
I think VSL would be a wise choice for doing something like that. The sections are smaller compared to those of GOS. Besides that they're recorded with not too much ambience, so they can be mixed easily with real strings. If you want the sound of a large violin section (say around 22) you can add 6 or 8 real violins to the VSL performance. You can add a few violas, cellos and basses as well of course.
I agree with Guga that you have to know the library well to get good results.
If you can record the impulse of the space where you record the live players, then you will be able to apply the same impulse to VSL using GigaPulse. Also, note the microphones used during the real recording and apply those as well.
By matching the space and microphones with GigaPulse, the mix between the live and synthetic music should be excellent.