What effects did Aeneas' journey have on him?
This question is not easy to answer as we do not truly get inside Aeneas' head in the course of the Aeneid. Vergil does attempt to convey his thoughts and emotions, but there is something very unsatisfactory in his efforts as Aeneas seems constantly to be driven by the need to fulfil his divine destiny rather than follow his own impulses and desires. The most obvious example of this is of course Dido, whom he leaves in a desperate, suicidal state in order to resume his journey to a new homeland for his people in Italy - on the orders of the gods (specifically Mercury in Book 4, if my memory serves).
However, the most charitable view of Aeneas sees him as growing to heroic status in the course of the his journey. At the beginning he is a very insignificant character - sleeping as the Greeks take control of Troy - who suddenly has thrown on his shoulders responsibility for the survival of his people. In this sense, his journey and all the trials and tribulations that he faces are a learning experience from which he emerges successfully, establishing his followers in Italy. He remains frustratingly elusive and dull as a character, but to take his achievement at face value, his travels teach him a talent for leadership which he certainly does not have when he awakes from a deep sleep to find the Greeks rampaging through a burning Troy. Thus his journey can be seen as (to use the modern cliche) a steep learning curve, dull as that may seem for an epic 'hero'.