FLASH memory cell degradation with use affects reliability, not response time. Any application level slowdown is due to filesystem fragmentation or poorly thought out indexing schemes. If you want the truth, straight from the horse's mouth, look at the technical briefs and application notes on various FLASH memory manufacturers websites.
Amazon claim you can turn an eInk kindle off by holding the power button for up to eight seconds depending on model. From personal experience, a K3 that has been shut down that way, cold boots when next activated, and if it is left unused, the battery seems to retain its charge for longer.
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