as far as things i would have actually liked to have seen "built" were political achievements, which would have served to centralize power and population, but that failed:
the 1883 elevated rapid transit (L) lines:
nextstl.com
included a line south, west, and north. there were subsequent, modernised versions of this plan that included more underground alignments. i believe it was put to voters two or three times.
in 1876, st. louis city suceeded from st. louis county, citing rural st. louis county as a cost burden and formed it's own urban county. under a 1926 plan and the bourough plan of 1962, would have re-united st. louis city and county into a municipal county like new york city. clayton probably would not have happened.
copyright bill cobb
earlier st. louis riverfront plan:
stltoday.com