Having a specialized saddle when you go up to level "cool amateur" or beginner, is not necessarily required. A good purpose saddle allows work on the flat, to chain the correct course. It is enough comfort to spend several hours outdoors. Better to focus a good purpose saddle, adapted to the horse as the rider.
Some people swear by the saddle obstacle, even for dressing or walking. Okay, as long as it is suitable! Attention, however, the presence of rear latch may interfere with training in downhill leg.
Dressage saddle is a case a little apart, not in fashion for so long. One swears by it recently. She appeared in the 70s in the pros, in the 80s among amateurs, and in the 90s for all comers. And honestly: 9 out of 10 times it is very poorly chosen and pose big problems.
It is true that a good dressage saddle gives the impression of having a position at the top, facilitates leg down, allows you to feel more clearly the movement of horses for increasing the close contact zone between the posterior and thighs the rider and the back of his horse. But it remains a very specific saddle, which is made up for sitting with a hip joint open and free, allowing only very moderate position in balance, let alone jump.
So on a young horse, his interest is limited (since mounts a rather young in balance, is not it), and a versatile rider, it is not used much. So if you have the means, you can buy two saddles, especially found the good of good quality market stools, adaptable for both the horse and the rider using various "tricks" (interchangeable panels arcade and refittables side horse, removable cleats rider side). You can also find fine used saddles. But better focus on mixed if not that of dressage.