DRanck
Here's someone that will break your concepts:
https://soundcloud.com/mattiaswestlund
 
Mattias doesn't use expensive orchestral libraries, he mostly uses Soundfonts! Checkout his articles here: http://mattiaswestlund.net/?page_id=29
What he does with those libraries blows me away.

Thanks for sharing!

I'll go in a totally different direction here... btw, DRanck... your example tied to the Mars photo just blew me away!  Really... I just put it on 10 and was swept into nirvana!
 
Anyway, getting back to the OP... I think we have TWO approaches these days... Sample libraries AND Phrase libraries...I have lots of both... So far, the discussion has centered on sample libs and this is the overwhelming body of work available today...You can easily spend S10K on the available options!!!
 
Now, if you're looking for "Authentic"... you can consider Phrase Libraries!  Personally, I think they are fantastic... real people playing real lines!...if you are looking for periodic orchestral contributions, or just want some amazing orchestral riffs to embellish your creations... Phrase Libraries, like Sonokinetic's Sotto, Capriccio, Grosso, and Minimal OR Native instrument's Action or Emotive Strings offer an entirely different approach... they include ACTUAL orchestral PEOPLE playing various riffs which can be combined, modulated, layered onto songs... REAL stuff that sample libraries don't provide...People are PooPooing these like they use to PooPoo sample libs, but they ARE Fantastic tools...AND THEY ARE THE REAL DEAL
 
On a third/different plane you also have riff generators, like Spitfire's Ostinatum Generator, which is available in their Albion Range of instruments (DRank... others????) which you can use to create and play phrases.... really pretty amazing, although the OG gui sucks from my vantagepoints... it is TOO small.  You might consider getting Albion ONE and dick around with the OG... you'll love it... it comes with OOOOODLES of OGs you can select and use to learn to make ur own.... then, consider some phrase libs...
 
Have fun... you can spend days sorting thru the above... I'd urge you to do so.... unless you are flush and don't mind spending a lot more for things you may find aren't useful...
 
 
 
 

Albion's Ostinatum is the bomb. Its a great tool.  I personally haven't found anything quite like it. I tend to use it as an idea generator. I've also used NI's Action Strings from time to time. 
 
Phrase libraries are definitely something to think about and yes, they are sometimes looked down upon (so what). It depends on what your goal is IMHO. If you want to create a good-sounding piece and do it fast, they can be a real help. If your goal is to create a piece that can be played by live musicians, they are not a good choice. If your goal is to learn orchestration, they are not the best choice for that either. Personally I use them as an adjunct to regular sample libraries and only where I think they provide a particular value. If phrase libraries help you reach your goals, use them!

bapu

DRanck
Here is an example of what can be accomplished with skill and patience: https://www.youtube.com/watch?v=9OsGjbl0vbY 

Cue batsbrew to say that it sounds fake and should have been done with a real guitar and amp.

nah, 
i got nothing to gain,
and nothing to lose.