This has been discussed on several Focus forums already.
Your car has three mounts. One hydraulic and two rubber. The rubber ones last much longer so I wouldn't bother with them.
The Hydraulic lasts about 100k miles (if that).
Also, make sure to change the passenger side engine mount (there's three)
I purchased my car also at 60k miles and thought the vibrations were normal...
After I changed it, the car became smoother in ways I never thought possible. It was like a different car!
It's really easy to change and with a floor jack and some common tools you can change it in less than 30 minutes
Only thing I'd STRONGLY suggest, is getting the FORD part only. Anything other than OEM and it's basically the same as a bad mount. These are actually hydraulic mounts, so when they go bad they leak the fluid out and transmit engine vibrations into the cabin etc.