That studying is invaluable when it comes to helping your model horse knowledge and vice versa! For those of us who have studied equine science at University one of the most valuable lessons was definitely dissection. Actually having the chance to see how the muscles and skeleton fit together on a real horse and understand the underlying structures is invaluable when it comes to judging a model horse. I would recommend everyone who judges or customises at least looks at drawings and diagrams of how the horse is made up, even if you don't want to look at pictures of (or even better see a real life) dissection.
Knowledge on how to correctly fit tack is also so important. If you have ever studied for your BHS exams or Pony Club badges you will know that understanding how to fit tack is a vital part of this. This is so so so important when it comes to performance, both judging and showing. If you know how to fit a saddle to a real horse then you can easily tell whether the saddle correctly fits a model horse! The same goes for bridles and other bits of equipment too. All that time spent in Pony Club learning about how many fingers each thing should be from each part of the horse is invaluable, put those skills to good use when you are judging a performance class.
Carrying on with the performance idea we come to rider's position. If you've ever ridden you will have had various things shouted at you about potato sacks and slouching and shoulders back and other things. Now look at the doll on the horse. Would you shout at her? Are her heels down and her shoulder's back? Is there a straight line from ear, shoulder, hip and heel? Where is her knee? What length are her stirrups? Are they suitable jumping or dressage length? Are her thumbs on top and her hands holding the reins? (ok as far as is possible with badly behaved dolls).
Then comes the inspiration part. I always think I can use model horses to help me study and often have done. A friend of mine once completed a custom where she had painted all the muscles of the horse onto the model, Breyer also did a similar model year's ago. If you are having to learn the names of all the vertebrae or which tendons and ligaments go where why not help your revision by also creating a really cool custom? The same goes for other elements of learning as well. You could build the ideal stable environment, thinking about the bedding, fixtures, size and everything else that goes into the perfect stable. Or you could create a horse sick pasture with a warning about various types of dangerous plants, adding them all in in miniature? See how much inspiration you can get just from attempting to revise things?
Other important things you'll learn that will help your performance involve how the horse moves and stride lengths. If you show jumping you'll know all about strides and pacing but it's amazing how many performance entries you see where the horse is just in completely the wrong place for the jump. Think about your model horse's stride and where you need to place them so they have the optimal take off for that jump. Each jump is different and will require a certain amount of height and width to clear it, all of that effects where you take off and where you land.
Finally, even if you've never studied anything to do with horses I would recommend that you get your paws on a Manual of Horsemanship. You really can't go wrong, not everything is strictly correct (just ignore everything about horse colour and go and buy something like the Equine Tapestry if you want to learn about that) but the basic information will help to give you inspiration and improve your in hand and performance judging/showing.