For what my opinion is worth, yes, I think there are definite thematic connections here! At the risk of talking under your research and thoughts thus far (which have the decided ring of a well-crafted discourse):
Contextually, this verse:
Luke 18:8b "However, when the Son of Man comes, will he find faith on the earth?"
comes at the end of a passage where Jesus is talking to his disciples about the "coming of the Son of Man", beginning in the previous chapter:
Luke 17:22 Then he said to his disciples, “The time is coming when you will long to see one of the days of the Son of Man, but you will not see it."
In spite of the tendency for us to separate chapter 17 from chapter 18, there are clear markers indicating the unity of everything said from 17:22 to 18:8, most notably the continued mention of the topic in 18:8b ("However, when the Son of Man comes...") as well as the phrase in 17:22 ("Then he said to his disciples..."), which is echoed in 18:1 ("Then Jesus told his disciples..."). Additionally, the parable in 18:1-8 is:
Luke 18:1b ...to show them that they should always pray and not give up.
Why would they be feeling hopeless? Because Jesus had just told them that the "taking" of this person and the "leaving" of that one was actually a reference to people being killed or surviving the events accompanying that Day:
Luke 17:35b - 37 [O]ne will be taken and the other left.”
“Where, Lord?” they asked.
He replied, “Where there is a dead body, there the vultures will gather.”
Additionally, ending the Day of the Lord discourse with a 'takeaway' on faith (i.e., Luke 18:8b) creates a bookend with Luke 17:1-19. Firstly, the admonitory illustration of the mulberry tree is in response to the disciples' statement that they lack the faith to carry out Jesus' instructions:
Luke 17:3-4 “If your brother or sister sins against you, rebuke them; and if they repent, forgive them. Even if they sin against you seven times in a day and seven times come back to you saying ‘I repent,’ you must forgive them.”
Secondly, this is followed by the story of the ten men with leprosy in which, interestingly, it is the man who returns to Jesus (as opposed to Jesus returning to the world), who is found to have faith.
On the back of this unity of 17:22 - 18:8, together with the 'faith bookend', the connection to Genesis falls into the lap, given that Jesus uses the both the flood and the account of Sodom and Gomorrah to illustrate the sudden and destructive nature of the coming of the Son of Man:
Luke 17:26 - 29 “Just as it was in the days of Noah, so also will it be in the days of the Son of Man. People were eating, drinking, marrying and being given in marriage up to the day Noah entered the ark. Then the flood came and destroyed them all. It was the same in the days of Lot. People were eating and drinking, buying and selling, planting and building. But the day Lot left Sodom, fire and sulfur rained down from heaven and destroyed them all."
Elsewhere in the New Testament, e.g., Peter's Day of the Lord systematic, if you will, in 2 Peter 3, we see clear allusions to Luke 18 / Matthew 24 / Mark 13 in terms of the content of the passage (and possibly even in the use of exact phrases and / or words, which I have not investigated), and note in particular the references to faith in 2 Peter 3:13 (with vs 12b as context):
2 Peter 3:12b - 13 That day will bring about the destruction of the heavens by fire, and the elements will melt in the heat. But in keeping with his promise we are looking forward to a new heaven and a new earth, where righteousness dwells.
This "looking forward to things yet unseen, in keeping with [God's] promise" is, of course a very familiar definition of faith in the early church:
Hebrews 11:1-2 Now faith is confidence in what we hope for and assurance about what we do not see. This is what the ancients were commended for.
Noah's faith is, of course, specifically mentioned in this passage:
Hebrews 11:7 By faith Noah, when warned about things not yet seen, in holy fear built an ark to save his family. By his faith he condemned the world and became heir of the righteousness that is in keeping with faith.
(However, these passage would of course have been written after Jesus spoke the words that found their way into the gospels, so 2 Peter and Hebrews would not have informed Jesus' words in Luke 18 in any way (unlike Genesis), rather the other way around.)
In conclusion, whilst the "favour" of Genesis 6:8 might not tie directly to the "faith" of Luke 18:8b etymologically speaking, the themes of judgement, rescue, faith, grace, promise and obedience ring loudly through Genesis 6 and Luke 17/18, creating thematic parallels that are echoed in Peter's second letter, as well as in the book of Hebrews, to name but two instances.