"I am talking about very important things."

Translation: Я говорю про дуже важливі речі.

[jmango2]

Does розмовляю not work in this case? Is there a difference in meaning between говорити/розмовляти?

[Vinnfred]

Generally, говорити = say, tell. Розмовляти = talk, speak, but only in the meaning of conversation!
So, They are talking = вони розмовляють, but She speaks three languages = Вона говорить трьома мовами