Sandbars are not a problem to get off, as you say, rbodell, particularly in tidal estuaries, but sandbars can be dangerous in traffic situations. But I'm sorry, I did not mention sand, you know. There's not much sand to be concerned with in the Sacramento - mud and rock, and old tress and wrecks, mostly. What you choose to ignore includes collisions and grounding on rock and worse caused by uncontrolled occurrences - these are very much easier to avoid, (note avoid) when there's an operable engine. Avoiding casualties is not realistically a matter of convenience, rather it is a matter of legal responsibility and common sense.
Sailing in congested and limited situations loaded with latent kinetics obviously calls for all the armamentarium one can muster. People get injured. Sail can fail from various causes and sometimes creates uncontrolled power -- which can be very dangerous. Delay in medical treatment can be the deadly result of failure to secure the full available armamentarium - including an engine. Obviously there are numerous situations in which an engine is "going to make a difference". Really, it's obvious to almost everybody.
"Local knowledge" is often the only kind that makes any difference, and it seems to be lacking in some people.
I don't believe that you, rbodell, have experienced this, as, if you had, you could not logically take these positions. (This is a compliment to rbodell, by the way, as it implies that he is logical.)
As most boat types know, doubling the number of engines doubles the probability of an engine failure, even more, actually, as people ignore problems thinking that they have a "spare". Therefore twin setups are a selling feature, primarily. I have had numerous pleasure craft, sail and power, and have never had a twin. On an serious voyage losing an engine on a twin means reduced control and can mean disaster, twins means reduced efficiencies and increased fuel requirements, fire danger, etc. Therefore sensible folks buy singles. At least they do around here. It may be different somewhere else - perhaps there are many inexperienced people in, for example, Florida - don't know. It's a foreign country and I won't visit there.
Singling out a slightly related idea and addressing that rather than an honest centralized reply is a technique in classical rhetoric. I believe that it's an aspect of paralipsis. Some readers might think that rbodell is engaging in this technique. Worse, some people might take the view that he has fallen into the ad hominem fallacy. Generally the resort to ad hominem is considered to be a good indication of a failure in logical argument.
Although rhetoric is inescapably a part of any usage of language, what seems to be more important in a discussion group that address technical matters is dialectic, which is what I am attempting here. I believe that it would be productive for us to move toward that.