I have a 12', 10,000 lb dump trailer that only weighs 2000lb, giving 8000 lb capacity. While I know that this is smaller than the 14,000 lb trailers you guys are contemplating, your payloads are only around 2000 lb higher given the heavier construction of the bigger trailers.
I use mine primarily for building materials, and when I built the house in CA it was very valuable for taking construction debris to the dump. About 100 trips in 2 years.
Since there was a quarry very near to the dump, there were a lot of return trips where I hauled gravel back rather than just bringing the empty trailer back. But, once that job was over and we moved to Oregon, taking any trailer to just to pick up gravel is a losing proposition. I can get 10 yards delivered in a tandem dump truck for a $70.00 delivery charge. This is 30,000 lb. If I take my trailer to the quarry, that is a minimum of 4 round trips, probably 5 since I try to stay enough under the max capacity to be legal all the time. I would burn more than $70 in diesel making than many trips, not to mention the value of my time.
Plus the delivery driver can chain his tailgate and spread any thickness of gravel I want, with expertise that comes only with daily practice.
If you need a dump trailer for other reasons, by all means get one, but my experience is that even with a dump, going to fetch gravel is not a very appealing proposition.
Don't need 10 yards all at once? The solution is simple. A gravel pile in an out of the way place is very handy to have on hand for many projects. I usually have a pile of 3/4 minus, and a pile of crushed clean for drainage.