yeah, it's oft-remarked but it's extremely silly how much memory and CPU usage have been inflated over the years. 256MB was just fine for gaming in the early days of XP. windows 98 or windows 2000 could run pretty nicely on like, 64MB - a lot of people ran windows 95 on 16mb even. that's a modern, multitasking desktop OS!
and today you can't boot shit on 16MB.even raspbian or something is going to croak even with XFCE and the lightest-weight setup you can do (short of raw terminal - I did get ubuntu server with fbdev running on a thinkpad with 256MB, although the mach64 driver is in an absolute state at this point).
(menuetOS is a fun regression along this line - a full multiprocessing OS with all the fixings, in x86/x64 assembly, that fits on a 1.44 inch floppy disk)
https://menuetos.net/
I know that a lot of that power and memory has been spent on isolation and security, but part of the reason we need that security is because we've turned the browser and OS into a sandbox running untrusted code loading off the internet. It is interesting to watch this video of linus getting a xserve running (challenging due to cert expiration, discontinued services, etc), and part of the OSX Server Tools suite is things like time machine backup host, ichat host (self-hosted XMPP chat server!) and so on, and the point linus makes is that apple saw the way the wind was blowing and decided it would be more profitable to sell the service than the hardware. And writ large that's the tradeoff we've made from the macos 9 era to the modern one. Slower, browser-based and cloud-based applications instead of self-hosted or local applications.
https://www.youtube.com/watch?v=eFnj7LvhvR4
Anyway yes, I have done the same thing as you and original OP and put a mSATA drive in an IDE adapter to get an old machine running, and used a SATA SSD to juice up a cheap laptop when my nice one died in grad school, etc, and a SSD and maxing out the memory (if possible) does make a substantial difference.
People usually tend to think like "it's an old machine, it is running slow anyway" but actually I think it's the opposite and you should think "it's an old machine and it needs all the help it can get". It has little enough processing power already, at least let it progress at the rate of processing and not spend 3/4ths of its cycles waiting for disk!