This is the same dilemma I faced myself when Regulus came out.
The additional articulations in FX Strings I are nice, and may be very useful. Half-tremolo is subtle, but it is subtleties we are talking about, with this kind of library. Very slow glissandos can be faked, but then they are no longer the real thing.
At the same time, this is the type of library that benefits the most from the deep reverb from the additional microphones. For what I've experimented with other Synchron libraries, I find both the Room Mix and the Decca mics channels to be already great choices. But the first one is not flexible, and the second one is not as enveloping as the full set.
Unfortunately, since this is very personal, it is a choice that you have to do yourself, with no help from the others. In the end, you will probably later purchase the missing pieces…
Paolo