I've encountered some examples of usage of the aimsir ghnáthchaite where I'd expect to hear the conditional tense. For example, on recording of a speaker from Connacht I heard:

Dá dtigeadh scabhait ghaoithe ar mo hata agus a chaitheamh isteach in do mhóinéar an gcoinneochá é?

If a gust of wind came and carried my hat into your meadow would you keep it?

I would have expected "dá dtiocfadh..." or some other construction in the conditional.

Was this usage more common once? Does it convey a different shade of meaning to the conditional?

Go raibh maith agaibh

It isn't imperfect tense but past subjunctive (foshuiteach caite).
Both tenses have the same form (imperative has the same form as well in 3rd person)
except for the verb bí (here conditional and past subjunctive have the same form: bheadh, whereas bíodh is used in imperfect/imperative)

The conjunctions dá and mura were followed traditionally by the past subjunctive.
Only the consequence of the condition was in the conditional.
Dá dtigeadh/dtagadh sí, thiocfadh sé freisin. = If she would come, he would come, too

Past subjunctive was replaced largely by conditional forms
Dá dtiocfadh sí, thiocfadh sé freisin.

This is similar in other languages (e.g. in German: wenn ich käme / wenn ich kommen würde = dá dtigfinn / dá dtiocfainn)
It doesn't convey a different shade of meaning.

Thanks for the informative and concise answer!

So glad to have read this!!

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