Writing to a magnetic storage device will not cause "wear" on the ability to store data, in fact, writing data to magnetic storage drives "refreshes" the magnetism of the drive. This is why Steve Gibson wrote Spinright. It reads the data, and re-writes it many times in order to refresh the strength of the magnetic energy.
Doing this to a flash drive will wear it down, this is because there is a difference in the way magnetic storage holds data from flash technology. Flash technology uses floating gate transistors that wear out over time, like if you bend a piece of metal back and forth enough it will snap.
The only parts in a hard drive that are likely to wear out from use are the motor and chips. This is why I've written to hard drive manufacturers like Seagate, Maxtor and Western Digital suggesting the mix of the two technologies.
I suggested they make a hard drive that has no moving parts but uses magnetic storage plates, with solid-state read-heads, one per sector, all addressed like flash memory.
These would be safer to store data on, last longer and if I had the skill or know-how to, I would patent it, but I don't so I just suggest it to others to get it out there.