I dunno about
completely useless...

Sure, anyone who has Muskets (and Cavs, lots of Cavs!) doesn't need Riflemen, but Policemen
can be quite useful in the more marginal semi-core towns (with ~60–89% total corruption), of which (on a Continental map at least) you should have quite a few by this point in the game.
Plus the AI looooves Nat, so you can almost always use it as trade-bait for any Civs who don't have it — e.g. after gifting up any less advanced Scientific Civs into the Industrial, any who get Steam (or Med) as their freebie, will almost certainly be willing to trade for it. And having Nat may then also 'distract' those Civs into researching Communism and/or Fascism (and then Industrialisation and/or Espionage), while you run down the RepParts/SciMethod-beelines instead, and (pre)build ToE and Hoovers.
Why would you have excess money? Why isn't all your commerce going into SCI% and LUX% (while the AI-Civs' GPT is paying your building and military maintenance)?
But if you
do have a huuuuge p-...ile o' gold, you could also gift some of it (back) to any surviving (and/or belligerent) AI-Civs at 10 gold per turn, to keep 'em sweet, while you prepare for blastoff...