What difference in pronunciation is there between "macię klucz" and "macie klucz"?
I find a big difference between the "-a" and the "-ą" sounds at an end of a word--there's a clear n intonation when "-ą" is used to denote third person plural. I can also detect a clear "n" when the "-ę" comes in the middle of the word (e.g., in "mężczyzna," the "-ę" sounds like "ahn" in the French word "manger." But when "-ę" is used to denote first person singular, I'm having a hard time picking that up.
I understand your question, completely. I find that when Polish is spoken, often, first-person vs third person of the word sound exactly the same. For example, a word like "get" in Polish (dostac and the "c" should have the dot above it) will "sound" the same in first person (dostaje - and the "e" has a tail on it) vs third person (dostaje - the "e" has no tail". However, when I annunciate the first person version of the word, I do include the "e with a tail" sound. I do not understand why it gets lost when most people are speaking the language.