The economics of buying the SE sections depends on what other VSL libraries you already have, and if there's any likelihood of you upgrading at a later date.
I already have Appasionata strings Standard and am very happy with it. I bought SE Strings 2 and 2+.for the Chamber strings and thought the App sordino would be a bonus. The problem is, not only do the SE sections contain fewer samples per patch, but the preset structure (eg the way portamento is introduced) is entirely different on the 2 products.The App sordino sounds very synthy to me, partly the nature of the sound and partly because it doesn't include the full performance legato patches.
I rather naively thought that the cost of the SE set would be deducted from a Collections purchase, but this isn't true either, for my €200 outlay I only get €100 discount off the FULL (extended) Chamber Strings collection, nothing off the standard collection. I should have just bought the Standard Chamber Collection to start with.
As the man said - "buy cheap, buy twice!"