I just changed mine after 4 years, with all year round riding, which in this country is either wet, cold or just shit weather.
It's all about the maintenance and how well it's looked after rather than mileage.
From experience it's normally tight links that tend to go first on a chain. I'm presuming you have the original chain on?
As long as you're not feeling any lumpiness at all then you should be okay, but as soon as it starts it will get worse very quickly.
I'd be more concerned about checking out the front sprocket nut if you're going on a long journey though, and personally i would want to change the whole lot while you're at it if you say the front sprocket looks worn, along with the modded wider 12mm nut just for peace of mind.