If it were me, I'd plug it. It sounds you don't push the bike in the twisties much if you are getting that type of miles out of a rear tire.
That being said, a plug is only as good as whoever installs it. Make sure the people who plug it are tire pros and have a good reputation of repairing tires.
If any of what I've said makes you uncomfortable in the least, just replace the rear tire with a like model. Which brand tire did yours come with?