Today the U.S. Treasury introduces yet another dollar coin. Unfortunately, it's just another facelift.
When the Susan B. Anthony dollar was introduced, the reaction was uniform: it was too much like a quarter. The Treasury interpreted "too much like" to mean "looked too much like", and switched to the Sacagawea dollar - golden in color, with unmilled edges. It was indeed more a more attractive coin, but the unmilled edges - otherwise present only on the penny and nickel - made it feel cheap. In addition, it shared the Anthony dollar's weakest point - the size differed from that of a quarter only in making it enough larger to be inconvenient.
You'd think that after two failures, the Treasury might realize that "too much like a quarter" meant "too close to the quarter in size". I think a lot of people might be happy to use a more conveniently sized coin - say, between a penny and a nickel in diameter, with twice the thickness to make it easily distinguishable.
But no, the new coin is the same old size - it just changes the picture to an early president instead of Sacagawea, and Liberty instead of a flying eagle. I predict the same level of acceptance - extremely low.
They're keeping the size to retain backward compatibility with machines that accept previous dollar coins. Changing the size as you suggest would mean having to retool all the machines that currently take dollar coins to recognize a new size.
That said, you're absolutely right. (And putting Washington on the dollar coin isn't going to make it less like a quarter.)
I understand the vending machine argument, and I agree that the vending industry - or maybe just the vending machine manufacturers - want the coins to stay the same size. That said, I suspect the number of machines doing a significant business from the Anthony/Sacagawea dollars is tiny compared to the industry as a whole, so they stand to gain a lot more from a dollar coin size that would actually be accepted than they stand to lose from transition costs.
It seems like "the experts" are now saying you'd have to withdraw the dollar bill to get people to accept dollar coins. They may not remember a case where a transition worked without withdrawing the bills, but I do - Taiwan got people to accept 1NT and 5NT (NT = New Taiwan Dollar) coins while still maintaining the bills through the 1960s and 1970s. I also don't remember people having any problems with using Kennedy halves and Eisenhower dollars when they were available - the problem there was that the government didn't want to make them, not that people didn't want to use them.
I don't think the machine manufacturers would be the major hurdle there. They would get to sell a bunch of new machines, or at least charge a bunch to refit existing machines. I think the obstacle is the owners of the machines, particularly the federal government. IIRC, all the tentacles of the federal government that have machines that accept money are required to have machines that accept dollar coins. This can get pretty big when you include outfits like the post office, and every machine that dispenses stamps would have to be replaced/refitted.
So even if the number of machines doing business with dollar coins is not all that large relative to the whole vending industry, they're disproportionately concentrated in the possession of the very entity that's making the decisions about how big to make the coin.
Maybe for me it's a holdover from when the silver coins were still made of silver, and had milled edges to prevent people from shaving the edges and selling off the scraps of silver. Pennies and nickels never had this problem because they weren't made from precious metals.
Of course, dimes and quarters probably aren't worth shaving any more, either, since they switched to copper cores some time in the 1960s.
Yes - they switched from copper to zinc with a copper coating in the early 1980s because copper was getting too expensive, but I guess inflation has caught up with them again. Personally I wouldn't have any problem with getting rid of pennies and even nickels, though the latter would cause a problem because quarters aren't an integral multiple of dimes.