Good morning :) I'm Dr. Sara - I'm a licensed veterinarian who works exclusively with dogs and cats. I'm sorry Dr. Carla isn't online right now, but I can give you my thoughts so that you don't have to wait any longer :)
There have been a handful of research papers published within the last few years that study specific breeds and their possible risks of developing hip dysplasia, elbow dysplasia, and various cancers. Those papers so far have focused exclusively on Golden Retrievers, Labrador Retrievers, and Vizsla dogs. There was a significant increase in hip and elbow dysplasia and cranial cruciate rupture in the altered Golden Retrievers, but less so in the Labs. There was still an increase for Labs, but not as significant as Goldens. The paper on Vizslas focused only on certain types of cancers, and did suggest that there was an increased risk for cancer after being spayed. Another recent study suggested that altered dogs were more likely to die of cancer BUT they lived longer than the intact dogs in the study. Keep in mind that these are a very few studies in comparison to 30+ years of veterinary experience and doctrine. Initially spay/neuter was needed as population control, and it still really is important to keep pet population curbed.
My current recommendations for my own clients is spay around 6 months of age unless it's a larger breed dog, in which case I tend to wait until about a year to spay/neuter - BUT there are a few caveats. The owners have to be willing and able to care for an intact animal - meaning that the pet is microchipped for identification purposes (because intact animals are more likely to run away/get lost as their hormones lead them to wander), the pet is under very tight supervision to avoid unwanted pregnancy or breeding, and the pet is not having any problem behaviors related to being intact (such as aggression, urine marking, humping, etc.). For smaller breed dogs, the picture is much less clear on what their long term risks would be spayed vs intact. No one has done the studies yet. The significant difference between the degree of risks between the Goldens and Labs does suggest that breed plays a tremendous role in what diseases are going to be helped/exacerbated by spaying.
What I can tell you is what I see routinely with intact female dogs. I see plenty of mammary tumors, some that the owners don't notice until they are too big to easily remove or they have already spread to the lungs. I see many dogs with abnormal or irregular heat cycles or false pregnancies that can make it difficult to predict when they will be fertile, and thus owners see accidental pregnancies and unwanted litters. I also see dogs who get life threatening infections of their uterus - called a pyometra. The pyometra is the big one that I'd like to avoid for all of my clients and patients. When the uterus becomes infected, it is an absolute life threatening emergency and requires an immediate spay - which is risky because the pet is very ill to start with. Risks of C-sections, pregnancies, mammy tumors, and pyometra, in our general opinion so far in the veterinary community, outweigh the risk of a routine spay in a young healthy dog.
I hope this gives you some more information to consider in making your decision. Please let me know if I can answer any other quesitons for you :)