Awesome guys. Thanks for the great responses.
If I've done all my research correctly, it seems the only differences between PF2.5 standard and Platinum are the model packs listed here:
http://line6.com/modelPacks/
Since I'm only one pack away (the bass expansion pack, which I doubt I'll get, but you never know), by owning all the other packs, I'm essentially buying Platinum for $100 by buying Standard (minus the bass expansion, just to be clear). This assumes none of my packs are bundled with the hardware, or I keep it plugged in all the time if they are.
There's no other differences in the core PF2.5 software, right?
This makes sense, and is really great for me. At least I don't have to pay for everything twice :)