Currently expecting my fifth :)
I think it depends entirely on how you are as a person?
If you don't mind noise, have a more relaxed 'outlook' on life, aren't a clean freak, and find kids rewarding, i'd say go for it.
I always found (with my four) they learn to lean on each other and help each other out so they are not entirely dependant on only mum and dad.... older siblings will help put on shoes etc.etc wipe tears, sort out squabbles - of course, you do have to parent them to become independant!
You don't need a house full of toys, its always fun as they have siblings to hang out with and we don't need to be 'baby sitting' them all the time.
The early sleep deprived years are always going to be hard - but it passes.
I know with me, even though I knew what the first years will be like, i just really felt strongly about just having one more.