Not sure exactly what you mean by demos... if you are looking for recordings made with LASS Lite there are several on the Audiobro web site. If you mean a demo patch or something like that, well, I'm with you all the way.
It is very difficult to make the investments in some of these higher end libraries because you can't try them first. Trysound is OK, but it still isn't the same as actually using the product for a bit.
Used to be that local music stores provided that service, but they couldn't compete with the on-line stores, who saved at least a little money by not having to offer demos, and the little stores went away. There's an irony there!
The 8Dio Adagio Strings includes Violins, Violas, and Cellos, and the Basses are due to be released the end of this month. It's a really strong library, but it is expensive.
Stresov did try to strike a balance between separate sections and ensemble patches, I'm not sure they hit the mark.
Cinematic Strings does some really graceful glissandos - not sure how much more portamento would buy you. Give a listen to their demos to hear it.
GPO is probably the easiest to use in terms of sequencing, but getting it to sound as good as some of the others is a LOT of work, which is strange, since I still use the original Garritan Orchestral Strings, and they sound amazingly lush. Too bad they were developed for GigaStudio!! Anyway - as the libraries become more capable, and therefore require a lot more in terms of controller messages, cut and paste becomes quite a bit more challenging!
I don't own any of the Albion or Symphobia libraries - that approach to sequencing did not appeal to me. Recently I picked up Orchestral Essentials, and I have to say, adding that to a project provides some really musical glue - makes it sound a lot more like I imagine it should.
As far as the KH interface - I'm surprised more developers haven't taken that same basic approach. It makes life so much easier when dealing with complex instruments.
Please keep us posted as you continue your journey...