I have rapture and dimension pro.
I have used some of dimension pro's string samples.
The "Gerritan Pocket Orchestra" patches are good in a pinch.
I am wondering, are the orchestral patches in Rapture pro a large improvement over the Dimension Pro patches?
Well I have the same, and agree. I also have the Rapture Session with some of the new factory content, and the string sections sound good there. Session seems to be lacking the woodwinds and brass, but I'm not sure about the full version. Dimension Pro has that somewhat covered in Garritan, which gets imported to Session.
The problem with using these synths for an orchestral arrangement is not the sound quality necessarily, but that they are not multi-timbral, so that you will need to load a new instance of the synth for each instrument that you want.
The ability to load multiple parts into one plugin instrument has a lot of benefits, but this usually comes with a hefty price.
When many folks hit this limitation they move on to a dedicated soft sampler like NI Komplete, or Sampletank. The serious pros that need everything seem to prefer EASTWEST or Vienna Symphonic Library. Plus the sample quality usually improves as you move up the scale.
Not owning any of these more expensive sampling options, I recently stumbled onto a deal for $1 to purchase AIR Xpand!2. The full retail on this thing is $99, but it often goes on sale. Check the deals section in the Cakewalk forums. It is a workstation rompler style synth with a four part multi-timbral setup. It has a ton of strings, brass, woodwinds, choirs, percussion, and a lot more. 2400 patches covers pretty much everything, including a lot of synth stuff.
Plus if you get Xpand!2, then you become eligible for the upgrade pricing to the complete AIR instrument collection which includes the sampler Structure with a 37 GB sample library, for around $75 total when it goes on sale. Structure is multi-timbral, loaded with great strings, woodwinds, brass, etc., plus you have complete control over all of the sample parameters. Plenty of bread and butter sounds.