I collect most Canadian coins from the 1920s or 1930s onward. I understand the poster's dilemma. For me it depends upon how much I am into that denomination and of course affordability.
I have quarters from 1937 onward. I am still missing the '47 Dot and the '73 Large Bust. I think I could afford those two coins but I am just not enough into quarters to do it.
I love the silver dollars and have bought the Arnpriors and the five versions of the 1965. Also some of the short water lines.
Pennies were the first coins I collected as a kid. Recently I bought the 1985 Pointed and the two harder to get 1965s. Since 2000 there have been some pennies not circulated that had special properties (like 2008 non magnetic) that might have been just available from year sets for example. I went after all of those if they were under $50. I do not have a 1955 NSF cent. I'd rather put that money towards some better quality silver dollars.
So you can see it is about trade offs. I cannot afford a 1969 Large Date dime. If $10,000 magically appeared in my mailbox one day, I would not buy that coin even though I have most other dimes from 1937 onwards. I'd get more joy out of 100 other high quality coins than that single one.