You can compare the patches of each product by clicking on "sample content" on the individual product page.
The patches of SE Vol. 1 - Strings are the same as SE Vol. 1 - except that you'll get ONLY Strings, hence the low price. Therefore, you can additionally afford to buy SE Vol. 1 - Strings PLUS, which will give you a lot more articulations.
If you compare the combined Solo String content of SE Vol. 1 - Strings and Strings Plus to the content of Solo Strings I Standard lib. you might think, that the latter does not give you much more benefit, in fact, there are even some patches in the SEs that are not in SS Std. (col legno), but there are some main advantages:
1. You need SS Std. to have the option to upgrade to Solo Strings Full, and the additional patches which are in the extended lib. are worth every penny. You cannot get them within the Special Edition path.
2. The Special edition uses 1 sample per whole tone while the Instrument Collections have 1 sample per semitone.
3. The Instrument Collections have more velocity layers
Beside that, of course with the SE Vol. 1 Strings you do get not only Solo Strings, but the same samples for the orchestral Strings as well. So you must decide if your afore mentioned string quartets are your main goal, or if you want to take a general dip into the vienesse world.