Yup, the plastic lenses are permanently attached to the face plate.
You can, however, disassemble it and clean the inside of the plastic if you like. Here's an instruction page I put on my web site that should be helpful:
How to Swap your gauge faces
The link for removing the cluster doesn't work, so here's quick explanation.
DISCONNECT YOUR NEGATIVE BATTERY TERMINAL BEFORE PROCEEDING.
The cluster is held onto the dash by two torn screws. One resides under an oval "vent" looking bit on the left side and beneath the emergency flasher button on the right side. Remove these covers and the screws.
You can then tilt the cluster and brow toward you on a towel.
Get out of the car and look through the windshield and see how the three connectors work. You move a latch and by swinging it out, it unplugs the cluster.
Once you have the cluster and brow out of the car, the page above will be helpful to pop the knobs off the front and slide the locks side to side on the back and the face with just fall off the front and you can polish it or clean it.
Hope this helps!