As for speech degrading, it is logical. (Hearing) People constantly get reinforcement of their speech patterns and pronunciation based on what they hear around them. That is why people who move to a different area often pick up a bit of an accent. It's hard not to with all the constant reinforcement of the accent in the new area. BUT, people also tend to have language patterns of the old place stuck in their brains. So my aunt who moved halfway across the country as a young adult gets asked by everyone out there "Where are you from?" but when she comes home, people she meets ask her "Where are you from?"
The younger you are when this happens, the stronger the influence of the new accent because your pattern/habit isn't ingrained as much.
So when what you begin to hear is garbled or muffled by hearing loss, THAT is the reinforcement you get as to language, so your own speech will start to move toward that "accent" that you hear. Maybe not ever be as unclear or identical to what you hear, because you spent a lot of time hearing your "normal" accent, but it will influence your speech. If you totally lose your hearing, and begin to get zero reinforcement, you will gradually begin to mis-pronounce things, and not really notice it.