Sorry for the late reply (1 year!),
but for what is worth to your question “does memorising such gems have an effect on your soul?” I would answer immediately yes.
I still haven’t finished with the Divine Comedy - though the memorization rate is fairly constant since when I begun:
I still have one year left to reach the end - I saw that somebody may object to such a slow pace - but why hurry? It’s not a race.
From my personal experience, the strongest effect has been the feeling of total, inner possess of such a treasure. Never, even with my most beloved authors, I felt this way: always there was the book and there was me - but always separated… to memorize something this way makes them to coincide, I dont know how to explain it better sorry.
Something else: the feeling that my inner spiritual space became fuller thanks to the presence of this poem. At every moment it can happen that an event, a person, something you’re reading, trigger a place in the poem that is immediately there, and it illuminates with a new meaning what is happening then.
Another effect - the total lack of boredom or moments during the day when the mind seem to switch off: the instant I get up from my bed I start the repetition on the last Canto, which I’m usually able to finish in time for breakfast (if I’m a bit late with it I recite loud the last part to wake up my wife: she seems to enjoy it :-). No more boring commuter travels to/from work: I always recite it loud while on the bike/motorbike: it is pure pleasure.
And a last effect: the pleasure derived from the constant toil. In a sense I feel it made me a bit stronger with myself, not allowing me in the last 7-8 years to pause an activity so strange.