I found an article that shows how to exclude external drives from Spotlight indexing HERE, which is completely useless if you have to do it every single time when you plug back in the external drive.
Is there any way to prevent spotlight indexing AT ALL TIMES on EVERY EXTERNAL DISK either new disk or previous used disk or whatever...?
A quick test shows that an external drive's exclusion will still be remembered when the drive is removed and then re-plugged in.
You'll find various other methods on these questions:
How to stop OS X from writing Spotlight and Trash files to memory cards and USB sticks?
Prevent Spotlight from indexing external drive
Avoiding Spotlight to spin up external drive
Though these all require intervention on each drive.
