Did anyone mention the Korg Classic Collection? 

I've wanted to grab a couple of those Korgs, especially when they are on sale like right now, but they still haven't updated the UI for higher res screens. 

I missed the pre-release sale of Syntronik, I hope it will go again on sale...

Uneven634
I missed the pre-release sale of Syntronik, I hope it will go again on sale...

Keep an eye on the KVR forum "for sale" posts.  There was at least one used license for sale over there this week.
https://www.kvraudio.com/forum/viewforum.php?f=43

I just came across this Sonar X2 vid which gives a sneak peak at a couple of nice plugins/synths which I'd like to get my hands on. Making a beat quickly is what I'm trying to adapt to doing, to get that unexpected inspiration if it starts sounding OK.
 
I see that the user is using Geist (superceded by Geist2), Kontact, TruePianos, Nexus and a couple of other things.
(I doubt if he was new to DAWs though, even if he was new to Sonar X2, apparently.)

GjB
I just came across this Sonar X2 vid which gives a sneak peak at a couple of nice plugins/synths which I'd like to get my hands on. Making a beat quickly is what I'm trying to adapt to doing, to get that unexpected inspiration if it starts sounding OK.
 
I see that the user is using Geist (superceded by Geist2), Kontact, TruePianos, Nexus and a couple of other things.
(I doubt if he was new to DAWs though, even if he was new to Sonar X2, apparently.)

Interesting video.  I think you already have the tools on hand to do that, without buying any new plugs, unless you just really want to.  Nothing wrong with that! 
 
Session Drummer 3, using the step sequencer to build up the drum beats.
 
Sonar X1 Tutorial - Creating basic drum beats with step sequencer
https://www.youtube.com/watch?v=py_xQgNQnjA
 
(Part 1) SONAR: Master Class - Drum Production Episode II
https://www.youtube.com/watch?v=HZiZjQAxjCw
 
Studio Instruments Strings, for the strings part.
https://www.cakewalk.com/Products/Studio-Instruments/Strings
 
Rapture Session, there are some decent piano sounds included in the factory library that should be fine in a mix.  You aren't going to be playing any solo piano here, right?
 
Rapture, Rapture Session, and Hybrid 3 for the synth parts.  Hybrid 3 is loaded with sounds suitable for this style of music.
 
Have fun!

Thanks abacab.
Very useful tutorials!
Thanks for the info. I don't play the piano, so no famous concertos coming from me in the near future..
Sonar rocks!

Rapture/Pro can be a good one for such most sounds, esp. with a few libraries.  I've got one of Biolab's atmospheric libs and it rocks - or rules I guess.  Not much use for it in rock songs.  Long evolving atmospheres and not pads.  Upgrading SONAR gives you Rapture (and other tools) which is probably cheaper than buying many of the mentioned synths.
 
But the main thing is even simple/free synths, with the proper programming, can make most of the sounds you mention.  But not as easily, and you have to learn synths like your guitars, which might not be of much interest to you.
 
@

Thanks AT. I expect I'll upgrade Sonar eventually when I can afford to. I might well upgrade my monitor/screen first to a larger one, primarily for Sonar.

GjB
Thanks AT. I expect I'll upgrade Sonar eventually when I can afford to. I might well upgrade my monitor/screen first to a larger one, primarily for Sonar.

Since you already bought Rapture classic, the upgrade from Professional to Platinum would add these instruments for you:
 
Dimension Pro, AAS Lounge Lizard Sonar, AAS Strum Session 2, AAS Ultra Analog Session 2, True Pianos Amber, and some additional Addictive Drums ADpaks.  
 
You would also pick up some additional effects and Pro channel modules.  You would need to weigh this upgrade decision with purchasing instruments individually that meet your needs.