I think this is an interesting question - and one worth continuing to ask. The techniques you’ve noted are certainly valid. I know that, at some time or another, I’ve employed each - resulting in, as you say, “various degrees of success.” I’ll add an additional restriction I impose upon myself - no national, chain restaurants. If I’m going to suffer through a lousy meal, I’d rather not know that before I enter a place. Any hope is better than none at all.
Like @HolyTerroir, I also will adapt how I apply different techniques in slightly different ways in different places. For example, crowds in a highly populated area often suggest more about trend than taste. Whereas, a crowd of folks at an out of the way, rural cafe shows a certain commitment to the spot (assuming that there are other choices in the vicinity). Likewise, a scan of the cars in the parking lot can help - license plates from the neighboring state are a good sign, more than one cop car - especially if they’re from more than one department - is an even better one.
Another, more general, thought on the subject is to keep in mind that the objective is to find a good meal, not necessarily a good restaurant. This tends to come into play most when asking advice from “locals”. Asking, “What’s the best restaurant around here?” is likely to get you an answer speculatively based upon what the person you ask thinks you would think is a good restaurant. On the other hand, “Where would you go if you really wanted a juicy burger?” might actually elicit enough of an honest response to help (I mean, even if the guy says, “I love Hardees”, you know to ask someone else).