As far as I know, no. The price is static.
And again, to be fair, while MOTU is decent, and I'm sure the demos/samples you've heard sound good, they're often professionally arranged, and you usually find achieving the same results is more difficult than you imagined. Also, bear in mind that stuff like MOTU and Philharmonik are kind of old/dated. I don't think either incorporates round robins, or at least if they do, then not very well. Plus, MOTU symphonic does not have loop points on their samples, so all your sustained patches have an ending point, so in some cases, you can't sustain a note as long as you might need to. Also, look at the size of the library. More samples = more realism (usually). MOTU is like, I can't remember, 7 or so GB while Kontakt or QLSO or Vienna are like 30+.
You seem to be overly concerned with using your computer's resources. While I appreciate where you're coming from, you're just going to have to learn to work around this issue. Your computer is fine. If you start to run out of memory, just bounce your tracks. This is nothing new. All kinds of remixers/composers deal with this constantly, so just learn to be smart with your plugins. If you expect to be able to have 3 of every single plugin you own open, with a crapload of processing, then you're going to have to drop about 10,000+ on a super computer.