Hi Aaron,
here’s another point of view …
After my SE libraries were just sitting unused on my shelf for years due to their limitations, I got the Woodwinds I standard a month ago and upgraded it now during the sale and I am more than happy that I did that. There are good reasons to consider the Woodwinds I library instead of the SE version since aside from the (probably less important) chromatic sampling it includes up to twice as many velocity layers - which to me makes a huge difference.
Yes one can combine solo instruments to form a small ensemble. With a MIRx venue (which in my opinion helps nearly as much to achieve realistic results as the sounds themselves) there are distinct (pre-defined) positions and eq-settings for first and second instruments that give a good impression of different instruments playing, even though it is the same patch. Transposing and tuning back by half a tone is another way to prevent the phasing problems mentioned above (since this way different samples are playing the same tone). So it is perfectly possible to work just with the solo instruments. The woodwind ensembles are nevertheless very nice, since they have a different timbre that is hard to reproduce when layering the solo sounds in unisono.
The extended library contains a lot of pre-recorded phrases like mordents, grace notes, … and fortunately one can indeed easily play these phrases without such separate patches (although they sound nice I generally don’t like pre-recorded phrases very much due to their inflexibility and probably won’t use them). The extended libraries include (in addition to very useful longer portato versions with faster attack than the sustained sounds) also far more performance patches, which are just spectacular. It is these patches (in particular performance marcato, grace and trill) that allow to realistically play faster phrases (including mordents, grace notes, runs, arpeggios, trills, …). E.g. the performance grace is far more than the name suggests: it is extremely playable since it has generally more velocity layers than the legato patch and sounds great for nearly arbitrary passages, so that (like the performance trill) it can be used for all kinds of applications.
In case you decide to go for single instruments, I would recommend to get the full libraries, since the patches in the single instrument standard libraries are not the same patches as in the standard versions of the collection libraries (like Woodwinds I), but rather the reduced SE versions (with fewer velocity layers)! Unfortunately, I did not find any information on this point on the VSL webpage and found it out the hard way out after purchasing single instruments.
Cheers
Kai