I've been using my X200 since I got it. Not only has it survived multiple falls from a 1.8m standing desk, it's still perfectly serviceable for everything I've needed it for. Most Thinkpads released since then are markedly worse, plagued with low-resolution or glossy screens. They've also removed the LED indicator that tells you whether the AC adapter is plugged in and when the battery level is critical.
tl;dr: sure there are newer machines with better specs, but nothing better in ways that actually matter to me.
I don't know about the X200 specifically but older ThinkPads tend to be really good with that. I have an X220 and it is easily the most serviceable laptop I have ever owned. It was super easy to upgrade the memory and add an extra disk. The battery is replaceable without opening the machine up and so it's easy to swap batteries if you use your machine for very extended periods of time.
Yes, that's another reason I've avoided upgrading--I really appreciate the ability to swap the battery out in the middle of a long flight without a screwdriver.
Basically everything in the X200 is user-serviceable; you can even replace the keyboard without taking it in, provided you can find the parts you need. The only thing I'd be worried about is being able to find new batteries for it; worth looking into before you pull the trigger.
tl;dr: sure there are newer machines with better specs, but nothing better in ways that actually matter to me.