Yes, change them once a year for max speed.

Probably would see a change on replacing those 6 year old rubbers (also, 2005? I thought LoTR was 2003).

I've heard a few formulas for when to change rubbers. Some say when the flipper rubbers are dirty, but that happens far too fast on my TZ. Some say that they should be changed when the slingshot rubbers, when taken off, don't go back to a round shape on their own.

It's hard to say exactly when you should change the rubbers - their performance is a function of the integral of an unknown, non-linear function of play, temperature, humidity, and other (unknown) factors - and even if you could predict the state of the rubbers, or if you were to measure their elasticity, it's hard to say where the line is to be drawn, because it's likely a reasonably smooth degradation. Likely, I say, because nobody (as far as I am aware) has studied it rigorously.

At the latest every two years for me. At least at the amount I play them. I think that is probably the limit of their life. My buddy shopped the Getaway I bought 3 years before I got it and the rubbers really were shot. Climate and amount of play probably has an affect.
If you can see fine cracking in the rubber, I would say it is past time.
Man, it is time to redo my LOTR.

I clicked 2-5 years but more often than not I sell the game before needing to change them twice.

Depends when they wear out or break. Depends on the environment the game is in, the amount of play on the game, whether the game is truly clean when they go on it, etc.

It depends on how often it's used...