You might get some "negative" feedback on this question.
Many breeders look down their noses at unregistered breeding stallions or horses that are registered with less-prestigious registries or papers.
Most breeders breed with the intent of "bettering the breed" and breeding the finest registered animals that they are able to. They desire to make sure that the resulting foal has everything at it's disposal to make it a marketable animal that will be valuable enough to prevent it from future misfortune (a registered animal may be ultimately less likely to end up in a feed lot or working some crappy pony ride, for instance). There are SO many inferior REGISTERED animals that to breed an unregistered animal just doesn't make sense. Particularly stallions, which should always be held to the highest scrutiny.
No one is going to say that your horse is inferior, or not correct, or not a nice temperament, because we haven't seen him in person and can't make that sort of judgement. But just because he is not registered properly in the first place sort of automatically makes him unfit to keep as a stallion in most breeder's minds.
Lots of puppy-mill or backyard breeders don't really care about registration or quality, and concientious breeders just get upset about that. They spend as much money as they can afford for the nicest stock they can find, and they put a lot of money, time, effort, and heartache into their business or hobby.
I don't have an opinion on the NSPR... I think it's a great registry for kids wanting to show the ASPC horses and have another set of classes they can do performance in.
For breeding purposes, the more easily a horse can be registered in a registry, the less prestigious it tends to be. If a "mutt" or "grade" horse can get papers, then the bloodlines are not as deep, and thus the whole point of the papers is sort of pointless. Papers are great because you can trace bloodlines very far back, but not if any old grade horse is in it.
That's just my opinion I suppose, and a warning to you that you might not get any responses that please you.
Andrea