IMO, a keyboard protector is a very good idea. I have the newest model MBP17. To protect the keyboard, I tore off a sheet of Saran Premium clear plastic wrap and, using a ruler and razor blade, cut the plastic wrap into a sheet measuring 4-5/8 by 11-3/8 inches. Using the same rule and razor blade, I sliced a piece of clear Scotch™ tape into two 11-3/8 by 3/16 inch pieces. I positioned the plastic wrap so that is just touches the edges of the depression (top, bottom, left and right) where the low-profile MBP keyboard resides. I attached one tape strip to the long side of the plastic wrap nearest to the display. That tape strip sits on the flat aluminum surface next to the point where the top surface curves downward to create the depression where the keyboard resides. The second tape strip is placed on the other long side of the plastic wrap, next to the track pad. Give the plastic a gentle tug to make it uniformly taut and flat, then press the tape onto the aluminum surface that separates the keyboard and the trackpad. If you do it right, the plastic wrap remains taut, barely touches to tops of the keycaps and is essentially invisible. Illuminated keys continue to shine bright. If you really want to seal the keyboard, apply 3/16-inch wide tape strips to the left and right side of the plastic. I don't do that. Saran Premium performs well; it remains flat, yet "gives" just enough when you press down on a key, so that no pressure is applied to the adjacent keys. Voila...
You shouldn't need to clean your keycaps or dislodge muffin crumbs from between the keys for a long, long time. And you can replace your makeshift keyboard protector with ease.
Estimated cost: $0.02
Estimated time spent: 5 minutes or less (how does that compare to searching for and purchasing a $30 silicone keyboard protector on Ebay, not to mention waiting days for delivery?).
Satisfaction level: high to very high