So said an old Scotsman. But if a muckle is worth less and less, then mickles start not to matter.

Decimalisation  in Britain would probably have happened of its own accord. Our old pound contained the seeds of its own decimalisation. There used to be twelve pence in a shilling, but twenty shillings in a pound, not twenty-four or twenty-one. (Twenty-one shillings was a guinea.) Assuming the same rate of inflation since 1971, old pennies would be as worthless as half-pences are now - except that half-pences aren't even legal tender. So it wouldn't have mattered whether there were twelve of them in a shilling or  a baker's dozen of thirteen. People would have thought in terms of numbers of shillings. Ten shillings - there used to be ten shilling notes - would probably have been given a name of its own, "double crown", say.

The law of Google-thwart says that this theory of mine is either wrong, or someone has thought of it before. A bit of googling lends it some support. 

A non-decimal currency is one which has sub-units that are a non-decimal fraction of the main unit. Today only two countries in the world use non-decimal currencies: Mauritania and Madagascar. In both cases, the value of the main unit is so low that the sub-unit is too small to be of any practical use and coins of the sub-unit are no longer used.

So is it inflation or utility? Well it's six of one and half a dozen of the other.

Feet and inches, pounds (lb) and ounces are different, sure as eggs is eggs. Like eggs, those things stay the same, whereas a pound (£) doesn't.

That puts me in mind of a song by The Undertones:

My perfect cousin

What I like to do, he dozen