I would suggest failures other than tubes wearing out are more likely to be the main problems.
I recently had a 'free' LG 42 inch in the workshop, it was only 18 months old, and the LCD panel was 'duff' - the original retailer had refunded 75% of the original cost, and the customer had bought a new Sony from us, then asked us to dispose of the old set.
So, been nosey, I took the set to pieces - initially it would come on, then after a couple of minutes part of the screen would go darker (obviously CCFL's going off), there was then a smell of burning, wisps of smoke, and the set would lose picture entirely.
Sniffing round where the burning smell was coming from I noticed (through a tiny hole) a bright red arcing, so presumed the PCB connecting the tubes was arcing across, so I decided to take it to pieces to have a look.
Because of knowing exactly where the problem was, I tried to disassemble it as little as possible, but I suspect it's far better to entirely strip it down.
The fault was duff capacitors, the little blue HV ones that always fail, there were nine of them each side, three or four had completely burnt up (destroying the PCB) and most of the rest were also discoloured.
So basically it was knackered, but I decided to try and put it back together, just to see if I could
I though it was going well, it was all back together when I noticed something on the bench - on closer examination it was an SM IC - when sliding the metal casing back over the insides, I had inadvertently 'shaved' an IC off the flexible PCB. This was when I realised I should have done more stripping down, and assembled it in the original assembly order!