Yeah but all the reasons you gave were about how it benefited them for you to ask for their prayers. I'm saying it benefits you for them to pray for you. And if that person is righteous, more righteous than you, then it is even better. And that's why the prayers of the saints are good. They are made righteous. The prayer of a righteous man is powerful and effective.
As for saints in general - a bit of a digression - but the scriptures say we will be like the angels. The promise to Abraham about his offspring has both quantitative and qualitative values - like the stars in both quantity and quality. As Ambrose of Milan says - "how did Abraham's progeny spread? Only through the inheritance he transmitted in virtue of faith. On this basis the faithful are assimilated to heaven, made comparable to the angels, equal to the stars. This is why he said, 'so will your descendants be.'" Everywhere in the Hebrew scriptures, stars are angels, sons of God are angels (for example, Job 38:7, Daniel 12:3, Rev 1:20 and 12:4)
Angels had jobs. The angels governed the heavens, the seasons, and the nations. In the OT we see that after Babel, the nations were assigned to angels (cf Genesis 10, 11:1-9, and Deuteronomy 32:7-9). These angels fell out of disobedience, and accepted worship from the humans they were supposed to guide - excepting Michael, who is the Angel of Israel (Dan 12:1). These are the demons the nations worship (1 Cor 10:20, Deut 32:17). The saints replace these fallen angels, and become patrons and active participants in God's rule and administration of His kingdom. For example when the apostles preached the gospel in, say, Thessaloniki, and those people throw off the chains of the demons they worshipped, they later had a new patron - St Demetrius. People have patron saints who pray for them, and are named after them and baptized after their name (1 Corinthians 15:29). So, when you know someone who has cancer, St Nektarios seems to have a particular blessing for prayers for people with cancer. Ask him to pray for them, and you add your prayers too! St Patrick is the patron of engineers, I ask for his prayers. And so on.