Aye, I just find longer runs so boring.. 20-21 is about as much as I can take, but then I'll race trail marathons and 50k's as training runs.. as long as they are fast running I think you get your long run benefit.. not say doing a 25 mile fell race. Last year I did rennsteiglauf 43k in 2:50, beautiful runnable trail race in central germany. With doing a race you get food and water support.
here the problem is they wont turn the water on in the water fountains until its guaranteed not to freeze, but this weekend we'll be 70F+ and by the time they turn it on it'll be 80F+ on the long runs.. so other races give you that support.