beautician it's really nice. My older 2 are girls and they very much wanted a little brother. There were tears of joy when we told them we were having a baby, it was lovely :)
They help entertain the baby a lot. And I think as he gets older they find more and more things to do with him. One is really mothering and wants to cuddle him all the time (much to his annoyance sometimes!) and the other is his own personal giggle inducing machine. She seems to have such a bond that they spend ages just laughing at each other. The girls love each new milestone and proudly show off their little brother to everyone at school.
So from that perspective a bigger age gap is ace.
I do sometimes feel like I'm constantly having to tell the older 2 to hang on, or I'll be there in a minute. And these days when I bf him I have to go to a different room to them as he's so nosy he just doesn't get a good feed otherwise. I think they understand though.
They have told us a few times they don't want anymore babies so I am a little worried about telling them about this one! Have you told yours yet or are you waiting post scan too?
The hard part of a bigger age gap I've found is school. Fitting school runs and homework, reading and swimming lessons and all the other activities that gradually creep up on you. Before DC3 if I was shattered we could stay in out pjs and get ready at our own pace in the morning. Post DC3 there was no luxury!
That's probably way more than you wanted to know!! 
I'll have a think about 17 month gap questions!!