So they give very little detail about the other houses, the structure of downtown, etc. at least partially because they have to fit Martin Harris' farm in the North and the Hill of Cumorah in the South into the representation as well. (Notice that given the completion of the Erie Canal up to Palmyra, which occurred in 1825, and the continuation of the canal beyond that point, the map cannot really be considered from 1820; rather it is an amalgamated view, temporally.)
There are modern depictions of Palmyra with historical sites drawn in, such as the following two maps (originally from here and here):
These maps work the amalgamation backward, but the "old parts" in the canal, and the change bridge and similar features, often post-date the Mormon era in Palmyra. Ditto for the famous four-church corner, of which only the Presbyterian church, built in 1832, dates from before the Mormon departure. Thus, they can again not be used to enlighten us about the way Palmyra looked when Smith Jr was there.
Now there is a historical atlas of Wayne County from 1874, which has a nice view of Palmyra, but its maps are sold by the Historical Map Company (here). That atlas is also available in the New York Public Library (here), but the prices are even steeper. That's about 40 years too late, in some sense, but it gives a better idea of the way the city was actually used.
And so the quest continues; maybe the friends on Quora have an idea.
Update: Quora pointed me to the maps in Daniel Burr's 1829 Atlas for New York, which contains Wayne county, among others (but already with the Erie Canal), and additional maps from the 1850s and 1870s for the specific area of upstate New York, on (surprise!) one of Dale Broadhurst's Mormon info websites.
While some of these maps can be purchased at the NYPL or at other institutions, the Old Map company is more affordable. Some of the atlases though, such as the Anderson one from 1800, are easy to locate with World Cat, but difficult to travel to (mostly fancy east coast universities).