If I remember rightly, the ideal recommended noseweight for a caravan is 7% of it's MTPLM (Maximum Permissable Laden Mass - or it's max weight in English!)
When we had a caravan, it's MTPLM was 1340kg (sad how I remember all these details...

)
So, divide it by 100 gives us 13.4, and times it by 7 (to give us the percentage) = 93.8kg
The hitch on the van was stamped as having a 100kg max, and our 4x4 we used to tow with had a max noseweight of 150kg. So, we were ok to go with a noseweight of up to 100kg.
If you go below this "ideal" 7% noseweight, it will obviously affect stability to a certain degree, so you just need to be a bit more careful when towing. I found this out when I was taking our caravan in for servicing - we had to empty the caravan 1st, and when towing it on the motorway to the servicing place, it seemed a lot more affected by passing wagons. As a matter of interest, I checked it's noseweight when I got to the servicing place, and it was just below 70kg.