This would be my ideal set-up for American cash and coin.
First of all, retire the penny, the nickel, and the dollar bill. The penny and nickel experience negative seigniorage, while the dollar bill costs more to create, maintain, and replace than does the dollar coin.
Secondly, remove repeat honorees on money. This frees up space to acknowledge the contributions of women and minorities. There's no reason to have George Washington, Thomas Jefferson, and Abraham Lincoln on both a bill and a coin.
Thirdly, introduce some logic to the size of coins. With the penny and nickel out of the way, we can resize the quarter to what the nickel used to be and then resize the half-dollar to what the quarter used to be, creating a system where coins of increasing size are of increasing value. This won't mess with vending machines, because they already recognize coins of these sizes. They would just need a software update to count the coins at their new values. This would also make it so vending machines can now accept half-dollar coins.
Fourthly, switch to non-metal and non-fabric content. Stop making coins that kill dogs when they eat them, and stop making bills that fall apart so easily. This would mean use of aluminum and plastics for coins, and use of polymers for bills.
Fifthly, diversify the size of bills to facilitate distinguishing one denomination from the other. This can be done so that they still fit in wallets and vending machines (at least for smaller bills, but I can't think of the last time I put a $100 bill into a vending machine).
Sixthly, stop trying to prohibit illegal activity through restraints on all commerce. This means creating larger-denomination bills; if you want to stop the drug trade, fix the hopelessness that makes drug use appealing. When the Federales last issued a $10,000 bill (in 1934) for public use, it had the value of $183,000 today. Conversely, reintroducing a $1,000 bill today would allow for the same concentration of purchasing power as carried by $54.67 in 1934. Instead of entertaining asinine ideas to make commerce even more difficult, facilitate commerce and fight crime differently. (Also, create a $200 bill to fill the gap in the current system.)
Seventhly, these are three options I think are nice: use the golden ratio for bills, link the obverse and reverse images better, and introduce some color distinctions, as well.
My final line-up would look like this:
- Ten-cent coin (18-mm. diameter, same as before): Franklin Roosevelt (obverse) and World War Two victory (reverse)
- Twenty-five-cent coin (21-mm. diameter, which is currently the size of the nickel): Susan B. Anthony (obverse) and Female Suffrage Movement (reverse)
- Fifty-cent coin (24-mm. diameter, which is currently the size of the quarter): John F. Kennedy (obverse) and the Moon landing (reverse)
- One-dollar coin (26.5-mm. diameter, same as before): George Washington (obverse) and the Great Seal of the United States (reverse)
- Two-dollar bill (66 mm. x 107 mm.): Thomas Jefferson (face) and Declaration of Independence (back)
- Five-dollar bill (70 mm. x 113 mm.): Abraham Lincoln (face) and Lincoln Memorial (back)
- Ten-dollar bill (73.5 mm. x 119 mm.): Alexander Hamilton (face) and the Treasury Department (back)
- Twenty-dollar bill (77 mm. x 125 mm.): Harriet Tubman (face) and Abolitionist Movement (back)
- Fifty-dollar bill (81 mm. x 131 mm.): Ulysses S. Grant (face) and the Capitol (back)
- One-hundred-dollar bill (85 mm. x 137 mm.): Benjamin Franklin (face) and Constitution Hall (back)
- Two-hundred-dollar bill (88.5 mm. x 143 mm.): Rosa Parks (face) and Civil Rights Movement (back)
- Five-hundred dollar bill (92 mm. x 149 mm.): Dolley Madison (face) and White House (back)
- One-thousand dollar bill (96 mm. x 155 mm.): Grover Cleveland (face) and good government administration (back)
No bill is longer than the current currency, and the two-dollar bill's height is that of the current currency. The twenty-dollar bill would be 11 mm. taller than it currently is, which is less than half an inch. I'm not sure how difficult it would be to accommodate that in current vending machines.