by the time you can use that many spies without getting in to trouble with your cashflow you could already have whiped a way that country without the use of spies...
So what would be the use of changing the spy settings??
Besides the fact that spies cost more money then they can steal (day profit of a city is less then the cost of the spy stealing it)
ok with sabotage it can be very very annoying
i have used 60 spies on one city... it took days to get them back to the stone age and worse a lot of spies got detected..
in the end it costed so much i could have easily build 1500+ artilery that would have been much much more helpfull