I think you underestimate the intelligence of the character.
I have made this point before, but the second trilogy had some parallels to the first trilogy. Lucas has to bring a new and younger audience with him on a journey towards darkness.
My 6 and 7 year old boys enjoyed Jar Jar and as they grew older have rather paternal affection for him now. They realise he was stupid and not a serious character, but they were brought into the story at that age. I myself was 7 in 1977 so there are some similarities with my journey through the original trilogy.
No doubt my boys will partake in some internet sneeriness of Jar Jar later in life, but they will always have a guiding affection for him. Darkness follows light, and it is only this contrast that allows the new trilogy to be so compelling to a new audience.