Thank you all for the ongoing input here. I thought after starting this thread I should provide an update on my decision and some feedback. I ultimately decided to go with VSL Dimension Strings and after a rough start I have come to both like and dislike it for a number of reasons, some of which you have all already pointed out. It's main weakness IMO are the legatos and longs. The attacks of the sustains and legatos are really bad and like others have pointed out require a ton of CC editing to create musical lines. VI Pro should have a provision to create these natural kinds of swells but it doesn't. The attacks of the non-legato dynamics patches sound much better, but they can't be used as the first half of a sustain and you are stuck with their baked in crescendos so they can't be used to fix the bad starts of the sustains. I really hope there are some ways to fix this as the sustains and legatos sound so so lifeless and the dynamics patches are too limiting with their baked in swells which can't be made into sustains.That is going to be a tough requirement to fulfill. Basically almost every aspect of strings playing and recording is very different between these two. Either you go for a detailed and well balanced sound with smaller sections, or you aim for a big, lush and smooth sound of film recordings. If you have the grit and detail, the rosin and the wood of ‘early’ music strings captured in the recordings you won’t completely get rid of it no matter the tools you use. And if you have, on the other hand, a silky smooth big sound there is no way to get the detail and finesse into it that is needed for classical music.
So, if you go for Dimension Strings forget about the lush Hollywood sound. Maybe you can approximate it, but it will be struggle and the results will never satisfy entirely. Hollywood Strings or CSS are much better choices for this. And conversely trying to approximate an ‘early’ music sound with CSS is a lost battle. Totally different timbre, wrong vibrato style etc. In short, it’s a completely different aesthetic.
If you want to go for some kind of middle ground Berlin Strings would probably be your best bet. But then again, for not much more money you could get Spitfire Chamber Strings (if on a sale) and CSS. Or for a lot less money Hollywood Strings and Light & Sound Chamber Strings. (The L&S Chamber Strings have a very nice tone for classical music, by the way. Unfortunately they are a bit light on articulations for this kind of music.). If you are really handy with mixing maybe LASS can be convincing in both styles.
It seems that you did your research and investigated the libraries properly. Now you need to make up your mind which sound you want, and which of the libraries is closest to that. My only advice would be to not think that you can bend a library into doing styles it was not created for. Depending on the library you can to a certain degree, but it will never be fully convincing and thus not satisfying in the long run. If you are very handy at mixing it’s possible that LASS could be good at both. But I don’t have it so I cannot say for sure.
DS's main strengths are the shorts which IMO sound fantastic. It also can do well for creating smaller sounding ensembles by using a few of the "individual players" but falls short of being able to isolate individual players with success especially in the violins and sustains or legatos which sound very much like multiple players even when isolating one player. And why oh why do so many of the violins sound like meowing cats (legatos)? Clearly there is still a lot more developers can do here to deliver the promise of Dimension Strings to the point where each player is good enough to isolate with success or for blending purposes. One way they could do this is by fully isolating the players, but having the group play and recorded at once with headphones so they can get the benefit of tuning and blending their timbre to each other and seeing each other but completely eliminating that bleed through that keeps the library from living up to its promise and potential.
It's been years since DS was released and I would be surprised if they made any more fixes for it (like fix all the loud and wonky legato transitions that sound totally unrealistic and all the bleed through between the players) but I think an update to VI Pro could extend the library much further. I have plenty of ideas on how VI Pro could be enhanced to make DS so much more usable, but that's perhaps for another post....
Regarding Divisi i still think its an important feature mainly because I like the flexibility in controlling the sound of how large the ensemble is and DS can allow for that to some extent. For classical writing realism is enhanced with controlling the size of the ensemble to suit the desired sound.
So I hope other developers are open to making their own Dimension Strings type of library but (or VSL is up to making a better version of it) because there is a lot of room for improvement.
I've been tempted to get Hollywood Strings to layer with DS but so far have not done it yet. My understanding is their "divisi" sections are merely different microphones of the same large ensemble. So the timbre is not smaller in the same way it is with LASS for instance. I wanted to like LASS but could never get over its sound in the demo's i've heard. It just doesn't sound the way I want strings to sound.