Hello Ozoner, good questions...
A few comments concerning your posting -
My position on the Risch case has always been, "Well of course, anything is possible, but some things rate a higher probability of happening than others." So, yea, I consider the botched abortion theory. I also put it way down the list of possibilities. I do hold the miscarriage theory higher due to its suddenness and unpredictability. It also seems to fit the 4-6 month time frame if there was an affair going on soon after moving to Lincoln. I also do not think anything with having a simple cavity filled caused or contributed to her mental confusion. The beer bottles/drinking topic has also made me think a lot. Martin accounted for the whiskey bottle yet, not the beer bottles. Did he know something? If he was quick thinking and covering for her, he could have just as easily accounted for the beer bottles as well...Yet, if Joan was the suburban housewife with the drinking problem, where would she hide the beer? And, why dispose of it in the kitchen trash can? This is one of those questions where neighborhood scuttlebutt would help. By the way, as I mentioned before, Lincoln was a dry town in 1961, so if she bought beer, it had to be next town over, Waltham.
I have always found her falling into a pit or construction site and subsequently buried a bit unbelievable. There was an air/ground search for her in the days and weeks that followed. I can't see someone the next day mounting his tractor or dump-truck and not seeing a body in daylight...
I don't know about the locked car question. Odd, in the picture you see LE outside the car, no car doors open. Maybe that is why the intact coat hanger is on the roof? to pop the lock. I know today, people are obsessive about locking their cars with the remote and the fact that we have more valuables in our cars today. But, were people that way about locking their cars in 1961??