I know that technically it doesn't add anything to the picture, but I do believe that you perceive the picture differently. I remember clearly the difference it made to put that screen on my first Mits. And I remember back in the day that some tv's came with a "high contrast" glossy screen usually sold as a "protective" screen. It just gave the perception of a sharper picture.
I am not sure BMX or I will agree with you, at least to the extent that PQ is actually improved. We will not disagree that YOU don't see an improvement, and may very well agree that the pic does indeed look different, but I'm skeptical that we will think of it as improved. I don't see any way that it can make it sharper, but maybe there is some special sauce in it that I don't know about.
There really is no such thing as a high contrast screen, whether for a DLP, or even a front projector. Sure, there are grey screens that are dubbed "high contrast", but they are not. They just make everything dimmer. The contrast ability is inherent to the display, and ambient lighting conditions. An overall dimming of this finite contrast range is used so that the bottom level, or minimum level of black is lowered. But, see, the whole contrast range is lowered.
This is how you check your lamp hours on the XX833 series:
MENU-2-4-7-0
The hours should be shown on the bottom left corner.
A quick google shows that a replacement lamp is VERY affordable, comparatively speaking anyways, at about $125.
When I was talking about all the people I knew who never replaced their lamp, well it is extremely obvious to me that they need to. I guess, to be honest, a couple of them are sort of on their last legs (or have now kicked the bucket), so the owner was right not to buy the lamp. But if yours is working perfectly . . .