I couldn't figure out how to do this as a full-length post, so this will be more of a "here's this clip, go watch it" type of post. I made a little compilation of openings to a few overtures by Broadway orchestrator/arranger Hans Spialek. Spialek was one of the busiest orchestrators in New York in the '30s and early '40s (he did all of Richard Rodgers' scores from 1936 to 1940, for example), and it seems like when he created an overture, he would work from one or more unofficial "templates" he had in his mind. So all his overtures tend to sound the same no matter what melodies he's working with:
Spialek's contemporary Robert Russell Bennett was more inclined to give each overture its own flavour, particularly when it came to the openings. (Bennett's overtures include many of the most distinctive openings, from the startling despair of Show Boat to the fanfares at the beginning of My Fair Lady. Which of the openings were his idea and which the composer's, of course, is hard to say.)
And speaking of Broadway overtures, this next one has always been one of my very favorite examples of the genre (more so, than, say, the overture to Gypsy, which I always find a little grating). The overture to Wonderful Town perfectly sums up the show's combination of heart, '30s nostalgia and parody -- ending with the "Wrong Note Rag" makes for an exciting but weird-sounding climax -- and is just generally a model of how to do a traditional musical comedy overture.
According to Steven Suskin's book on orchestrators, most of this overture is the work of the former big-band arranger Jack Mason (whose other notable uncredited arrangement was for "With a Little Bit of Luck" in My Fair Lady), with a few bars of transition music contributed by Joe Glover and the show's credited orchestrator, Don Walker. The songs used are "Wrong Note Rag" (fanfare), "Swing!," "Ohio," "My Darlin' Eileen," "It's Love," and "Wrong Note Rag" again for the finale -- in other words, a cross-section of all the different musical moods of the show.
(Just as most composers didn't have time to do their own orchestrations, they didn't usually write their own overtures. The only overture Leonard Bernstein did himself was the deservedly famous Candide overture, which takes a different approach by treating themes from the show in a quasi-symphonic way, rather than the Broadway medley style.)
This performance, by Simon Rattle trying his hand at crossover, is a little stiff in spots (especially in the version of "It's Love"), but it's the only fully professional performance of it online, so: