At the risk of being flamed...If it's "just" for the foaling experience, then I think you are breeding for the wrong reason...jmho. I know you've talked alot about her behavior and how difficult she's been to work with in the past, and along with her less than desirable conformation, and build, those are all traits that can be passed on to her foal...you are wanting an athletic foal, who can jump and do things mom can't do, but you've got to look at mom; if she can't do some of those things, do you honestly thing a foal out of her will be able to do them any better than her, no matter how nice the stallion you breed her too is? A stallion will only be able to improve so much on your baby...he's only half the picture, here...your mare is the other half.
Now if she had really desirable conformation; nice hip, good shoulder, good legs, etc, along with really nice temperment, THEN I would think about breeding her, regardless of her grade status, because then you would likely get a foal that has those desirable traits as well. However, because she doesn't have those, you are taking the chance of having a foal that has crappy conformation, and a hard to work with attitude...regardless of how lovely the stallion's confo and attitude is.
To respond to the text in red: yes her conformation is not the best, which sort of pushes me towards the "don't breed her" side. She does possess some other traits I am very pleased with. He eagerness to work, when we're both on the same page. I have complained about her being hard to work with, but I mostly blame my behavior now that I look back on it. She only reacted "badly" or "negatively", because I as a handler/rider was screwing up. I don't blame her for her actions, I now believe they were reasonable due to the circumstances. Mom (Savannah) can jump, and depending on how she does this summer at local shows, plus the vet check for breeding stability will be the factor if I decide on breeding her or not. She's the only pony I've ever been on that tries to cut goats, or herd them for that matter. I would like to do something like team penning along with hunter/jumper, but her size kind of.. depletes(? Am I using that in the right context?) that. She jumps no problem, ponying off of other horses or ponies, works the goats, and even hauls little kids around. Last summer I taught my friend how to w/t/c on her, before she became "the wretched mare" (which I think is because of the saddle not fitting right, or the rider's incompetence [?Right context?]).. Let me stop before I start to ramble off.
Responding to the bold text: I know what a crapshoot breeding is, even with two "good" horses.
Ultimately - whatever the vet recommends I will follow. I will take his (or her, depending on who sees Savannah) veterinary opinion [for soundness and breeding capability], and their personal opinion. Otherwise her placing this summer in shows will also determine if I feel she could produce a foal that could lead a career in that discipline.
I'm not just some 14-year-old saying "Oh I want a foal! I have a mare so that means she can have babies! Yayy let's breed her and have babies!" - no. I want to fully think this through and I will not "do something" until Savannah proves herself. :)