Is it safe to delete files in this Garmin Express folder?

I generally delete all but the last two or three, "just in case".  By the way there is also a considerable amount of other stuff that can be deleted, again keeping just the last two or three.  I prepared a thread on this topic over on another Garmin forum.  See http://www.poi-factory.com/node/50977.  In the Windows paths I reference you will see the pipe "|" separating folders.  That is because that forum does not accept the backslash.

Thanks, so deleting these files won't affect Basecamp or the Garmin Nuvi device?

I can't speak to use with Basecamp as I don't use it but I use GE with three different devices and have no issues.  Since these are remnants of prior updates I doubt you would have any issues with Basecamp.  As an experiment blow away the oldest and then retest things.  It should be in your Recycle Bin if you need to get it back.  If things work OK, after a few days then remove the next older and again retest.  Keep in mind your free space on your storage will not change until you clear the Recycle Bin.  Read my content at the link I provided as there may be more to be cleaned up.