The dime is a cupro-nickel sandwich, where once it was silver. The quarter dollar, half-dollar, and dollar coins once were silver. In fact, the "Spanish milled dollar" or "piece of eight" or "peso de a ocho/ peso de ocho reales" served as the basis for the U.S. silver dollar, which had to be the same size, weight, and purity as the Spanish. It was legal tender into the 1850s, perhaps a bit like these newfangled Bitcoin type ideas and what not?
The nickel, thankfully, was always just nickel. The penny was once a huge copper coin, and became gradually reduced in size until it finally became zinc with a copper cladding after 1982... Now the zinc is worth more than the penny is worth. And people hoard the things in jars in every home and remove them from circulation.
The Sacagawea dollar led to the U.S. President du jour dollar... Literally every single POTUS was to grace the currency, including, say, William Henry "Tippecanoe" Harrison, POTUS for all of a few months, his successor, the "accidental POTUS" John Tyler, Martin Van Buren, James Buchanan... Millard Fillmore ... Warren G. Harding ... Calvin Coolidge ...
I think that bi-metallic coins where an inset of a very different metal, or by now, even ceramic?, might make for a coin that would not be confused by the user like the 1979-only Susan B. Anthony "Carter quarter" given formerly as change at USPS, or, perhaps, the brass/bronze color of the Sacagawea and POTUS dollars. They've already got different state quarters and now different parks and whatnot... For the record, I'm not opposed to putting flora and fauna on currency, and witness the success of Canada with the "loony."
Change simply weighs too much, wears holes in the pockets, and jingles when you walk... Let's make light-weight coinage of some high-tech but cheap material, and size the coins by denomination---five cents--ten cents--fifteen--twentyfive--fifty--a buck--a two buck coin--five dollar bill, ten, twenty, fifty, etc. etc.
If actual persons are to be honored with a place on the currency, maybe have a rotating set of options a bit like the POTUS dollar fiasco? The US mint has already changed the colors of bills, so people won't get confused by the "all green, all the same size" bills... Get people to actually look at what they are paying for purchases with?