Wow. There are some excellent, well thought out posts on this thread.
I like the idea of keeping your present .38 handy and also buying a shotgun for more firepower. In my own home, this isn't much of an issue because my home is very small and no one lives here but me. I spend most of my time in one of two rooms and the shotgun is never far away. But, your situation is no doubt different, so you can carry the .38 and still have the shotgun available if you can get to it.
A note about being blinded and deafened by a gunshot. First of all, if I was empolying a gun in a defensive role in low light, I would want a light. I am not saying that it would be impossible for a senario to devolop where I didn't have a light, but I plan on using a light. My shotgun is equipped with a dedicated light/forearm so odds are, I will have a light. I also keep a Surefire three cell flashlight on my nightstand. So, that takes care of being blinded. When I turn on my light, my night vision is gone anyway. As far as noise, I have no experience being in a defensive situation. But I have fired large bore rifles at game animals. I never noticed the shot. All my concentration was on my sights and the animal. I have fired two and maybe three shots and have no recolection of hearing the sound of the shot. I dont' know if this translates over to firing a handgun in the house in a defensive situation or not, but I tend to think that it does.
As far as running a shotgun in the confined spaces of a house, I think that is a training issue. Police and military regularly use long guns in clearing houses. I have taken a few classes at a big name school where they teach the technique of the "indoor ready" position. They do say that it isn't always the best technique and at times it might be a good option to transition to your handgun for really tight quarters but as homeowner we probably are going to only have one gun, so this probably doesn't apply to us. But, you can manuver around your house with a shotgun and do well with it. If the senario dictates that you are going to stay in your bedroom behind a locked door, this isn't an issue. If you are manuvering through your house, it is only an issue at corners.