You can calculate it !
Take your power usage and compute the cost over a year.
I will soon add a SSD because i finally moved from a RAID 1 to RAID 5 (so more HDDs), it consume more electricity.
I can measure how much power it draw because the server is on a smart plug. I calculated an additional 20-30€ a year of electricity, adding a SSD for read/write cache would allow the HDDs to stop spinning, make things faster and will be cost effective over a few years.

Consider that a new power efficient CPU may be cheaper by consuming less electricity over a few years!

Got acquired and rised price.

When you are bored, backup a VM then hard kill it and see if it manage to restart properly.
Software should be able to recover from that.
If it doesn’t, troubleshoot.