MacOS – Clearing NVRAM on Yosemite shows password entry

In a word, no. If you are concerned with the contents of your machine being compromised should the machine be stolen a better bet may be to encrypt your drive with FileVault (assuming you are or intend to upgrade to using Lion). Even if the firmware passwords was irreversible, it would not stop someone simply taking your disk out and reading another way. The only benefit I can see is preventing a theif from being able to ever use the mcahine he just stole, but frankly this won't help stop your laptop from being stolen in the first place, although it probably would result in it getting binned if it was, rather than re-used and potentially identified at a later date via it's serial number etc.

Modern Macintosh computers store very little information in PRAM so resetting it is seldom a useful troubleshooting step.

Have you checked the condition of the battery using System Information? (It's in the Utilities folder and also accessible from the menu: [Apple] > About this Mac > More Info… > System Report —assuming you're running Lion)

If you're seeing Service Battery under the Hardware > Power:Battery Information/Health Information section that's probably your issue.

You might improve the battery life with a System Mangement Controller reset. Assuming your MacBook Pro doesn't have a removable battery, the SMC reset procedure is:

Shut down the computer. Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected. On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time. Release all the keys and the power button at the same time. Press the power button to turn on the computer.   Note: The LED on the MagSafe power adapter may change states or temporarily turn off when you reset the SMC.