I have been looking into the parable of the prodigal son in Luke 15.11-32. I am now fairly certain that the younger son represents the (Sadducean) priesthood, and the older son represents the Pharisees for the following reasons:
1. Though not so depicted in the Gospels, the Pharisees were "a lay movement in competition with the priesthood" ("Pharisees," ABD, 5.289).
2. The Pharisees were known for their strict observance of the Law. The older son viewed himself as a faithful Law-observer (15.29).
3. The older son was "in the field." E. P. Sanders (Judaism: Practice and Belief, 181) says, "Let us recall that priests and Levites were forbidden to work the land.... They were not tied to farms, as many Pharisees were...." So a priest or Levite (and presumably Sadducee) was not permitted to be "in the field." The Pharisees were known for having such occupations.
4. The younger son is said to have been "dead" but is now "alive" (15.24, 32). This is a picture of Jesus' resurrection. The irony here, like in RM&L, is that the Sadducees denied the resurrection; but when Jesus is raised again, he becomes the new eschatological high priest and reconsecrates the priesthood to God (cf. Lk24.50-53). Therefore, the younger son in the parable undergoes a change of heart. This is the change in the priesthood from a Saducean perspective to Jesus' perspective. The "father" describes the return of the priesthood in terms of resurrection. And he is addressing the older son, representing the Pharisees, showing them that this new priest is different from the established priesthood of their day.
5. The younger son is clothed with new clothing upon his return. This is reminiscent of the re-clothing of Joshua the high priest in Zech3.1-5. Interestingly, the high priest of Zech3 is named "Joshua," the equivalent of "Jesus." If it can be shown that Jesus is meant as the one bringing the priesthood back from the Sadducean demise of the pig-pen, then it isn't so ironic that Luke's Jesus is alluding to a story about JOSHUA the high priest as found in Zech3.
6. This might be another instance in which Luke lets his background story inadvertantly shine through. Note that in the parable the older son complains that the father "never gave me a kid, that I might make merry with my FRIENDS" (15.29). In Zech3.8, the angel of the Lord says to Joshua, "Hear now, O Joshua the high priest, you and your FRIENDS who sit before you, for they are men of good omen...."
7. The older son complains that the younger son had "devoured [the father's] living with the harlots" (15.30). This was a common complaint concerning the priests (e.g., TLevi 14.5-6). The Pharisees (the older son) was at odds with the Sadducees (the younger son) and would have made such complaints about them, demonstrating their illegitimacy.