I don't think "sparring" would give much that you wouldn't get from normal randori/jyu waza training. Although I can see how people I know would end up using awful bad technique which would be bad for their aikido in the long run. If you told me I was going to get mugged and gave me the choice, I'd personally take three hours of Kihon Gi over a month of "sparring."
We don't do sparring as such in our dojo, instead we do circles. One person stands in the middle of the circle and the students on the outside take random turns to attack them. The grade and experience of the person in the middle will affect which attacks are allowed and whether people are allowed to attack from the back and sides.
The whole point of it is to make you do something, anything. You really learn the difference between a static technique and a dynamic one. You learn which techniques work against different speed attacks. Most of all you learn to get off the line.
When we started to do circles I had a real problem (as did most people) in that I would step off the line and my mind would go blank. Needless to say if that was a real life situation it would be bad
It isn't sparing, it isn't really randori, it is sort of a combination of the 2 and it is very usefull.