Trying to maximize speed up to those levels for storage space for files like pictures and similar is probably wasting money unless you have some special circumstance where your photos are gigantic (RAW) and you want to see them as fast as possible on click. Else, the economics of HDD storage even if HDD (relatively) slow will be great for any such storage.
IMO, when to chase theoretical maximum speeds is for those niche situations where you are doing lots of big read/writes to complete a task: video editing is one such task... making MANY track music recording/production is another. Or if you are one of the relatively rare people where time (measured in seconds) really is significant money, that may justify such a target as well.
For browsing files like photos and similar, the good old HDD will be fast... NOT maximum fast but not aggravatingly slow either. If you need faster than single HDDs, get a RAID HDD setup and that will speed things up even more.
What others have offered applies: use folders to segregate types of files. Individual drives would likely be overkill except for very unique circumstances. If you are going to buy multiple drives, get a RAID enclosure, put all of them in there, set up as maybe RAID-0 for speed or RAID-5 for (self) backup (security) and that will give you great speed at relatively low total cost... especially versus a bunch of individual SSDs or a RAID SSD setup.
The "scratch" drive concept gets at the idea of wanting to do something- again like video editing- where you will be doing heavy read-writes to the drive. So you might move the project onto the speedy SSD-RAID or single SSD as your "scratch" do your video editing on it and then move it back to big HDD storage when you are done with the intense work. You reference Logic Pro and Plugins and those projects can be complicated enough to benefit from some very fast SSD-RAID or single SSD "scratch" especially if RAM is small and thus swaps will be used in a big way. However, again, you can store big Logic projects in big storage on HDD or HDD-RAID and then drag the project you want to work on now onto faster storage "scratch" while you work on it... then back again when done to free up the scratch space.
Chasing max-speed SSD for everything is going to be expensive and likely overkill. From what you've shared, you probably should go with a hybrid option of some fast SSD/SSD RAID storage for working "scratch" and big HDD/HDD-RAID for general purpose storage. Either way, be sure you can buy some backup drive(s) too because no choice is good without a backup to restore if any SSD or HDD setup fails.