I don't have VSL CFX, but I do have VSL Bosendorfer Imperial. The full library is significantly better than the standard in my opinion. It adds the additional close mics for a far more realistic and less tinny experience. Also, if you play with headphones, having at least one surround mic on makes a massive difference for the realism and fullness of the sound (make sure to set a delay of about 30 in the sound settings for the surround mic).
Having said that, I think the strongest point of the VSL pianos is their room sound, and you can get a lot of bang for your buck out of the standard library. If your goal is just to render performance pieces later, standard might be good enough. But for live performance (and of course, better rendering for the final recording), full is the way to go.
I will point out that there is no disadvantage to buying standard and upgrading later.
While I can't guarantee it, there are often good Black Friday sales, so it might be worth waiting if you can stomach it.
However, if I could do it again, I'm really tempted by the new Bosendorfer 280. I'm not sure I can justify it at this point with what I already have (I'm personally hoping for an upgraded Steinway), but I think they really nailed the note separation and clarity for their newest release.
If you need additional incentive, I'll add that I love VSL as a company and am excited to support them. So, go full and help support the good guys.
I want them to keep pumping out cool stuff!