I still don't have the full Kontakt, only the player, but I was tempted by a $125 crossgrade deal earlier this year from a licensed instrument.
I had already picked up the full ST3 last year for $60. So probably someday I will get Kontakt, but just don't feel the need yet.
ST3 is a good rompler. The included library is enough for writing songs, or sketching up arrangements. You would probably want real musicians to record with if you get really good or successful anyway.
Plus I have crossgraded from ST3 to add Syntronik and Miroslav Plilharmonic CE for cheap. Those libraries can be imported into ST3, so you have a lot of multi layering options in ST3 with all that included. It pays to wait for the deals.
Windows 10; with instruments from AIR, Ample Sound, AAS, Cakewalk, IK Multimedia, iZotope, KV331, NI, Seaweed Audio, SONiVOX, TAL, Tracktion, u-he, Way Out Ware, XLN, others...