"That's a dilly of a question!" :) Yes, "dilly of a" can be a synonym for excellent and perhaps delightful, and it has been used that way since at least the early 1930's, but dilly is older than that.
And then there's the lullaby:
Lavender's Blue (Dilly Dilly)
Lavender's blue, dilly dilly,
Lavender's green
When you are king, dilly dilly,
I shall be queen
Lavender's green
When you are king, dilly dilly,
I shall be queen
Who told you so, dilly dilly,
Who told you so?
'Twas my own heart, dilly dilly,
That told me so
Who told you so?
'Twas my own heart, dilly dilly,
That told me so
Call up your friends, dilly, dilly
Set them to work
Some to the plough, dilly dilly,
Some to the fork
Set them to work
Some to the plough, dilly dilly,
Some to the fork
Some to the hay, dilly dilly,
Some to thresh corn
Whilst you and I, dilly dilly,
Keep ourselves warm
Some to thresh corn
Whilst you and I, dilly dilly,
Keep ourselves warm
Lavender's blue, dilly dilly,
Lavender's green
When you are king, dilly dilly,
I shall be queen
Lavender's green
When you are king, dilly dilly,
I shall be queen
Who told you so, dilly dilly,
Who told you so?
'Twas my own heart, dilly dilly,
That told me so.
By the way, I dug around and dilly is used in Australia as a combination of daft and silly...and that makes sense...but daft and silly in an entertaining, delightful way.Who told you so?
'Twas my own heart, dilly dilly,
That told me so.
So! Have a dilly, dilly day!