From my point of view, the internal cleaning is worth it.
A few months ago I bought a pt-40lc12 floor model. I had been keenly looking at this model for some time but didn't want to spend 2K on it, but the clearance price was really unbelievable. So with the assurance I had 2 months to decide or bring it back, I brought it home.
Once I got it home and started tweaking, first thing I noticed was the picture had a grainy look to it. Come to find out, this floor model was missing the dust filter and had been sucking in dust for who knows how long. So I called Sears service and they sent out a guy who seemed very knowlegable about the set. He took the front off and cleaned the whole inside. I guess there was dust everywhere from the missing filter which had something to do with the grainy picture because it looked great after he left. Sears even sent me 2 filters and the whole thing didn't cost me a dime.
Now if he had left me a spare bulb..