Like propped up with crutches, sounding a little wheezy with memory issues? No, not really.

Electronics on motherboards are solid state... meaning they are built up from a series of logic gates and components that manipulate the binary bit i.e. a '1' or a '0'.

If a motherboard is not looked after, parts will fail from a list of causes...

Static
open circuit (tracks)
short circuit (tracks pulled high or low)
wrongly inserted part, or orientation
failed part needing replaced
... dare I say it... human error!

I'm even sure folk use their boards as mid-air projectiles from time to time.

Point is, after power is brought into the system and fed onto the main power tracks of the motherboard, it is then subject to signal conditioning. If the signal can not be conditioned as per the system design, you have a fault, and for the motherboard to work, the fault must be fixed.

You forgot the number one culprit: heat.

Heat? I never had a single old computer failing due to heat.

If a computer starts acting wonky, it's most likely related to power supply or bad caps.

Bad caps fail due to heat. Chips often fail due to heat. Transformers fail due to heat (although they usually last much longer than caps). Keep your retro gear cool and it will invariably last longer.

The physical effects you listed are a concern, especially when installing or removing components, but heat is a relentless killer of components which takes it's toll regardless.

To the OP, yes, this can be a common issue with old hardware. This is why learning how to test voltages and replace capacitors is a very good idea. However, some new hardware comes with similar reliability due to incompetence or cost cutting, so it's probably more accurate to say it's an issue with hardware.

This behavior looks like you have unstable power, maybe bad caps, bad power supply..

Yeah, 15years old PSUs or older should always be checked especially when you have stability issues. My PCChips 486 was behaving oddly sometimes (it even crashed). At first I thought that since the board is from a crappy brand it was the culprit. However the PSU smelled very bad and so I opened it to clean it completely and even though the caps were not bulging, to me they didn't look right (and they were from a cheap brand). I decided to replace all of them and now the computer has no more stability issues. Every time I recaped a PSU, the computer it was running from became more stable