After mulling over the same question for months and months, I bought a new PJ lamp in January just before the recommended 1900 hours arrived. There was no problem with availability for my five year-old Sharpvision and the bulb arrived direct from Japan in about five days (Yes, I was an early adopter of 720P and paid a lot for the priviledge).
I figured it this way: A PJ lamp lasts me nearly five years. Within that time, 1080P PJs will improve, HDMI 1.3 will arrive, and prices will come down (I don't have to be an early adopter all of the time).
With only 300 hours on your Panasonic, there is really no rush at all to go out and buy a spare lamp. Just sock the money away, add some cash from time to time and enjoy the Panny.