Should I replace all my ignition coils?

I have a 99 Maxima. About a year ago a coil failed, and the repair
shop replaced it with an aftermarket coil. It was #2, and the problem
went away.

Few weeks ago all of a sudden I am getting the exact sympton again,
engine knocks and vibrates somewhat and lack of power during
acceleration. The code said it is #4 coil.

I went to the Nissan Dealer and got a coil and replaced it myself. It
cost me $110 and the problem was fixed. Both #2 and #4 are in the
front.

My car now has 2 new coils and 4 old coils. Should I just buy 4 more
coil and replace all of them? It is kind of expensive, all 4 would
cost me $500. (The #1/3/5 costs $117).

I am thinking I should do that rather than waiting for the remaining
ones to fail and then replace it, since the Maxima is known for its
defective coils. But $500 is not cheap, and if the remaining ones are
good, it seems money wasted.

Are there places where I can buy Nissan coils at a cheaper price? Do
aftermarket coils works as well? Local pepboy said they have it for
$86.

Raymond