My eldest will be 12 (11.5 now) and the youngest is 9 and then this one's due July.
Can't really answer as I'm not there yet, but I'm hoping the bigger gap will be good.
Certainly I have found it useful during the early pregnancy as I have felt so sick and tired, I'd have been terrible if I had younger kids to look after. At their age though they have been able to occupy themselves and not need as much supervision etc.
However I didnt plan to have such a big gap, though I do think it'll have it's benefits.