Questions from 21-st century's Milinda
I'd hazard a guess that if the Ven. Nagasena were around today he might respond with something as follows:

1) Just because you don't know that you have a problem doesn't mean there isn't one.

2) One cannot conclude that something in the past didn't happen just because you don't remember it. For example, I don't have any memories of being an infant or being born but that doesn't mean that I never was.

3) One should be concerned about Nirvana because it is not some sort of prize after death, but a reality that is fully realizable in the here and now.

4) One should strive for enlightenment through meditation because meditation is a necessary part of the spiritual practice. Without it one cannot expect to attain anything.