I guess this is a general issue: a solid state drive will dramatically improve the performance of the operating system first and foremost, and of the MC program, and any other program, that is for sure. I was not convinced till I tried, and upgraded my OS hard drive to a solid state. I could not believe how much better was the performance with same motherboard, same processor and same memory. I have also revived an old laptop to make it run decent again replacing the hard drive with solid state.
I am talking about Windows installed directly on a PC, not on Mac, through Bootcamp.
I am not sure if Bootcamp will activate all the features of a solid state that makes it faster, like "TRIM" or "Rapid mode". I would say, if you cannot activate these options under Bootcamp forget about it, you will get a marginal improvement that will not justify the investment.
Plus, each solid state drive comes with a mirroring program that makes it easier tomake the change, you create a mirror image of your current hard drive on the new solid state, than you just swap drives. Not sure if this mirroring works on Bootcamp properly.
About the library? Well of course it will run faster and more reliable on a solid state, but you will have to spend a significant amount of money to have the space required on a NAS, not to mention that you will need a special NAS for solid state drives.
What about your network components? are you sure that those are not the culprits of the low performance you mention?
I would say, before spending any money look carefully at ALL the components of your system, not only the MAC hard drive or the NAS and determine what is the bottleneck. It may be very well be your router, or NAS network card, or Mac network card, it may be very well be Bootcamp itself. Network components evolved exponentially from 2010. And any operating system and program installed on an emulated drive (what Bootcamp is doing) will always run slower than installed on a dedicated "native" drive.