Darn, had something typed up and lost it.
Ah, the previous champions who were invited for the 30th running. I can definitely see your interest in doing this. It's surely a great honor to be offered an entry as a previous champion and I'm sure it's hard to pass up running. I think I know who you are and you are a very experienced runner. Deep down, I think you know whether this is something you should do or not. I'd hate to get in the way of someone accepting an honor of a type I know I will never get to experience. Personally, as I know myself, I know a marathon on what you have done so far would be a disaster for me so I wouldn't do it. However, we are two different types of runners. You have always been able to do things that I could only dream of on training that would leave me desperately lacking.
Whatever you decide, I hope you have a great weekend. You've earned all the attention/adulation you will receive.