I love Dimension strings for what they are. They are not big lush strings, but they are the most detailed and expressive library I know. Also it's the best for divisi parts. I don't think DS alone could replace a 60 pieces strings orchestra though. The low register (celli and bass) can sound pretty big but the high register will always sound thinner than a real 16 or 20 violins section. But I love the sound I can get with DS alone with a bit of EQ to smooth some mid-high frequencies and some exciter to bring up some (smooth) brightness.
Other things to consider is the amount of articulations in those libraries. Appassionnata is the VSL string library that have the smaller amount of articulations (even if it as more articulations then most of other companies lib.).And DS is the most detailed one. For exemple, instead of one simple tremolo patch you get fast and slow tremolo. And having every strings position is reaaly nice, specialy the legato patch on the violin's G Strings.
But... If you already have LASS, maybe you should check for a complement instead of a substitute.
I use DS on top of other librairies (Orchestral, Appasionnata or Spitfire's Mural Strings) to get a big section plus more details or to do divisi. It should fit nicely with your LASS library too...
Not having violins II is not a big deal for me since I'm panning everything with MIR and I almost never write Vls I + Vls II in unisons. They have made some Violins II patches in Appassionnata but it's based on the same source samples.