Not sure if this thread is somewhat pointless now since the competition's over, but:
It's a soundfont player. It plays soundfonts
You don't have to buy the soundfont player. There's plenty of free ones, such as this one.
In fact, you can find a massive number of free and cheap VSTs and samples all around the internet. Which is why I wouldn't really recommend that you bother upgrading to Signature. While it's definitely brilliant value and it definitely comes with some awesome stuff, I'd recommend just getting Producer Edition (If anything, for the automation clips alone. I jumped straight in and bought Producer Edition, but I couldn't possibly imagine using FL without them. Plus the playlist. I have no idea how fruity edition even works without a playlist.) and then buy whatever cheaper/free VSTs and samples you need.
Instead of spending the extra $100 on signature, you could get a symphonic library like Garritan Personal Orchestra for $150, or Philarmonik Classik for $130 (Or if you're made of money, the full Philharmonik for $230). If you're planning on making more symphonic and classical music, you'll probably want to get a decent orchestral library.
Or, y'know, an electric guitar is cool too. You could just get one of those.