SSD drives are a lot less likely to fail but they can fail and so you still want to have your eggs in more than one basket. There is also a cost factor. A 1TB SSD sells for $700. For $100 I can buy two 1TB hard drives and mirror them as you are doing.
With a laptop having the boot drive be a SSD is a different matter as it speeds up boot times which with Windows is a big plus. Half the power consumption for a laptop can also be from the demands of a hard drive so a SSD extends battery run times significantly A laptop can also can be recovered without worry about losing critical data if you put your important data on external storage devices.
For traveling it is cheapest to simply take enough flashcards to hold the image files that are captured. Then the risk is diluted by virtue of having a dozen flash cards instead of a single device that can fail or be damaged or lost or stolen.