Okay, I openly admit that I made a mistake on Matt. 24:34, thinking without checking that the word there translated "generation" was the Greek genos, but it's really a synonym, genea.
Here is the definition of genea from the above-mentioned Gingrich's lexicon (leaving out all the references): "clan, race kind; perh. nation. Generation, contemporaries. Age, period of time. Perh. family or origin" (p. 41). Other lexicons have a very similar entry. Also, as with genos, there is a much wider range of meaning than the English "generation," putting to the lie the idea that the Greek doesn't help us in Matt. 24:34. It actually expands the need for interpretation.
I was surprised to see, contrary to what I thought (and may have posted here), that genea has the meaning of "race." So really, it is quite all right to translate it in Matt. 24:34 as "race" rather than "generation." It has a more subtle nuance: all of those born to an original ancestor. So the nuance here is that the "race" in the verse is specifically Jews, who were descended from Jacob, rather than other Mid-easterners.