I would never use a spinning HDD for anything again consumer-based except a NAS that needed 10+ terabyte capacity, and then I'd keep it somewhere where the noise and cooling profile worked, i.e. not my living room.
Why? I understand if we're talking about 3.5" drives, the most modern ones (helium) seem to be too noisy to live in the same room as audio equipment, but 2.5" hdds are very quiet. OK, people will talk about the write life, but if it is mostly for reads, what is the problem? Still less than half as expensive as SSD and seems to work well enough for most media (90mbps transfer speed on 3/4 full drive). My problem (latency) seemed to be one of Windows power management - everything is pretty snappy now I turned the spinning down off.
Obviously an SSD is a must for the OS or anything that needs large throughput, but how much stuff is that? I like the idea of not wasting money and feel that for uses like media, SSD is still too expensive.
Really comes down to how much capacity you need. My music alone is currently around 20TB...
That does seem a huge size, have you considered trying to 'double blind' some 320kbps mp3 or similar compressed formats? Sounds like you might have a lot of 24bit/96khz stuff too - I think that stuff just tends to hog drive space, not sure if there is any audible improvement, especially when for much music I personally find I can't tell much, if any, difference between a 320kbps mp3 and wav....ymmv, of course.