First of all, I think there's a distinction between a general reward (heaven) and specific reward (holiness and merit). The parable is talking about general reward, i.e., all who come to God, regardless of how long they were Christian, will receive the same reward out of our Lord's generosity for "the last."
There is evidence, however, for a specific reward. Our lord talks about those who break certain commandments being called "least in the Kingdom of Heaven" (Mat 5:19), compared with those who keep them. There are people who are holier than us, and assuming that they die so, they will be more righteous than us in Heaven. This isn't a competition though. I think of the Prayer for Humility, which says
<Jesus, grant me the grace that others be holier than I, provided I become as holy as I should.
In terms of living a life full of pleasure and then doing a final deathbed conversion, I think there are several problems with it. First, there's no guarantee that you're going to die on your deathbed. You could be killed by a car, murdered, etc. Secondly, since sins harden the heart, a person who has spent their whole life in sin would have a hard time finding contrition outside of a fear of death. In addition to this, God knows the heart of every man, and so He would judge those who sought to "rig the game" accordingly. The mafia members who think they can live a life of crime and hedonism and wash it all away with a half-hearted confession are mistaken. If someone was truly and sincerely repentant on their deathbed, they wouldn't be looking at it like it's a "get out of jail free card," but sorrowfully wishing to serve God, and even take back all the things they did if they could have. I'd say they deserve to be given eternal life just as much as us.