Leaflet supports a detectRetina option on tile layers that will shrink the tile size and load more tiles but give the appearance of higher resolution maps.
This map is created by stacking the gray basemap, median household income map and the map labels for the gray map. The 2 basemap layers are loaded with detectRetina:true while the labels are not, giving the appearance of a high resolution basemap.
The draw back of this method is that for each normal map tile you are now loading 4. Comsuming 4x the bandwidth.