Well I have been producing music using synthesisers now for the last 37 years and been paid very well for doing so as well. So I know a thing or two about synths, more than most. One of the things I have realised is there is
NOT one synth, hardware or software than can do it all. End of story. Many make the claim and like to think it but in fact it is actually impossible. And even if there was such a thing it will still suffer from everything sounding just a little similar that comes out of it. Plus there is always something it won't be able to do.
The key is texture and texture comes from using multiple instruments that all have different sonic signatures. Some here will agree. I have got well over 100 virtual instruments plus 10 serious hardware devices and collectively this will blow Omnisphere right out of the water. Between all of them there would be over a million patches I would say. Plus they all sound a little different. Sure many things cross over and overlap but overall the range of sounds becomes staggering once you go down this path.
The only thing here though is that you have to learn all the OS systems of everything you have and that can be daunting at times.
The OP may not actually need Omnisphere but simply a great instrument that will cover very well what he wants and needs. That is the key. And he will get that for way less than the cost of Omnisphere. One day I will buy it too. Because yes there will be some real nice sounds in it that I can use for sure. I will wait for the gig first and let them pay for it though.