I took my 4 yr. old anode rod (which looked much worse that the 1 in the picture) from my Trailmanor into the local RV dealer to get a replacement. The lady there said that she could sell me 1, but that I had a lot more life left in the 1 I had. If it gets down to looking mostly like a thin wire, then it is finally toast. I know that they are fairly cheap, but $12 or so over maybe a life expectancy of a 1/2 dozen years is $70 or so of money in my pocket. Besides, I sold the Trailmanor.
I do think it is very important to check that puppy every year, ideally when winterizing.
On a like note, while replacing the thermostats and checking the elements on my home water heater this week, I looked into the tank to check the anode rod there. Before rinsing it off with a stream of water, it looked like it was coated with clear Jello or something......yuch !!! After rinsing it off, it looked more like the used anode rod in the above picture. It was just sitting there and doing it's duty of giving up ions it's lifetime of galvanic exchange.