As expected from a theory which some of the finest minds in the field helped to shape and perfect, the Two-Source hypothesis does have some admittedly pretty strong arguments for it. Aside from the ones you mentioned, there are also these:
1.)
Luke’s order. Supporters argue that Luke’s arrangement of double tradition material is inexplicable on the assumption that he knew Matthew. While a lot of double tradition in Matthew appears in five blocks of thematically related discourse (5-7, 10, 13, 18, 24-25), the same material appears in Luke’s Gospel in a different format, much of it in a big central section: the travel to Jerusalem in 9:51-18:14. The point is felt so strongly that supporters of the theory have posed this question: if Luke knew Matthew, why would he choose to ‘disrupt’ and ‘demolish’ Matthew’s clear and concise arrangement and scatter the whole thing all over the place? Case in point: the Sermon on the Mount/Plain. If Luke knew Matthew, authors would argue, why would Luke have wanted to disturb and spoil what is usually regarded as one of the finest religious writing of all time and place different parts of it in an unconnected form throughout his Gospel? The implication being that if Luke was aware of Matthew’s Gospel and yet consciously tampered with it, he was a very poor writer.
An important aspect of this argument is that Matthew often seems to find an appropriate Markan context for double tradition while Luke does so rarely. The preaching of John the Baptist and the Temptation, which feature both Markan and ‘Q’ elements, occur in the same context across all three Gospels, but afterwards, Matt and Luke usually diverge in their arrangement of double tradition pericopes.
2.)
Luke’s ignorance of Matthean ‘additions’ to Mark. A typical example given is Matthew 12:5-7, which is a Matthean addition to the parallel account in Mark 2:23-28.
Matthew: At that time Jesus went through the grainfields on the Sabbath. His disciples were hungry, and they began to pluck heads of grain and to eat. But when the Pharisees saw it, they said to him, “Look, your disciples are doing what is not lawful to do on the Sabbath.” He said to them, “Have you not read what David did when he was hungry, and those who were with him: how he entered the house of God and ate the bread of the Presence, which it was not lawful for him to eat nor for those who were with him, but only for the priests? Or have you not read in the Law how on the Sabbath the priests in the temple profane the Sabbath and are guiltless? I tell you, something greater than the temple is here. And if you had known what this means, ‘I desire mercy, and not sacrifice,’ you would not have condemned the guiltless. For the Son of Man is lord of the Sabbath.”
Mark: One Sabbath he was going through the grainfields, and as they made their way, his disciples began to pluck heads of grain. And the Pharisees were saying to him, “Look, why are they doing what is not lawful on the Sabbath?” And he said to them, “Have you never read what David did, when he was in need and was hungry, he and those who were with him: how he entered the house of God, in the time of Abiathar the high priest, and ate the bread of the Presence, which it is not lawful for any but the priests to eat, and also gave it to those who were with him?” And he said to them, “The Sabbath was made for man, not man for the Sabbath. So the Son of Man is lord even of the Sabbath.”
Luke: On a Sabbath, while he was going through the grainfields, his disciples plucked and ate some heads of grain, rubbing them in their hands. But some of the Pharisees said, “Why are you doing what is not lawful to do on the Sabbath?” And Jesus answered them, “Have you not read what David did when he was hungry, he and those who were with him: how he entered the house of God and took and ate the bread of the Presence, which is not lawful for any but the priests to eat, and also gave it to those with him?” And he said to them, “The Son of Man is lord of the Sabbath.”
Other examples given are the Walking on the Water (Matthew 14:23-31) and Peter’s confession at Caesarea Philippi (Matthew 16:17-19). The question asked is, why would Luke have omitted this fresh Matthean martial, if he knew Matthew’s Gospel? It would of course imply that if Luke was ignorant of Matthew in passages like these, he was ignorant of Matthew everywhere, which would make the Two-source theory necessary in order to make sense of double tradition.