>>>So, these current-generation 500+ GB 2.5" magnetic drives can suffer some sort of soft failure which greatly reduces their performance but doesn't make them actually "fail" per se.
>>>
>>>I don't know if this is relevant to your case - in the cases I saw, once the performance dropped it never came back, even after cold rebooting. Still, I thought I'd mention it in case what you're seeing is some intermittent or "early warning" case of the same thing.
>>>
>>>Replacement HDs are cheap these days (even SSDs are reasonable), it might be worth replacing that drive while it's still "functional" and you can successfully clone it.
>>
>>As the machine is currently not in heavy usage, I am unsure if I should upgrade from 8 to 16GB plus 1 TB SSD at least. It is only a 2.4?GHz I5 (cores not often taxed to the max even with that old generation) 15', while there are some offers for brand new double core I7, 16GB, smallish SSD plus 1TB HD 17' for 900€ including VAT. Currently not needing the 16GB by using some older 32-bit VM for most small tasks like surfing or office tasks, but newer software more and more targets only 64 GB, which run better if given at least 4GB each.
>
>Putting in an SSD would likely change some things for you:
>
>- CPU utilization: you would see that increase, for shorter bursts - less CPU idle time while it waits for disk I/O. Older machines actually become CPU-bound more often (but for briefer periods) if you upgrade with an SSD
>
>- Responsiveness while running VMs: an SSD's vastly higher (~100x) IOPS performance means running (effectively) several "chatty" Windows OSs (host + 1 or more VMs) simultaneously will feel much snappier
>
>- With #2 above you may find performance OK if you let a VM use its virtualized paging file, so you might be able to get away with less RAM per VM

Currently I usually have 3 VMs loaded besides the "work" task: mail, office and browsing are split up due to security worries (office due to using software eligible to vote in most countries...). Using 32Bit VMs and sizes betwen 768 and 2GB this is comfortable and leaves me enough for 1 heavy VM if I need it, as long as Win VM are not higher than Win7, often XP. But Win10 is not running well under 3GB, same as for most 64Bit OS I tried. And Chrome not supported on 32Bit Linux hints at me things will continue in that direction.

Loading 3 GB just to write some text seems silly for those remembering 8Bit machines and turning out some code or a letter - my writing speed is not much higher in this decade, as I had loads of shortcuts back then and sharper memory ;-)