Is there a difference between $hash{ key } and $hash{'key'}?

Just the visual ones. (I consider the latter more cluttered.)

As the chart indicates, the "autoquoting" has extreme precedence, so you don't even have to worry about using a key with the same name as an operator.

$ perl -M5.010 -e'$h{ die } = 1; say "ok";'
ok
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