Each programme has its own benefits. If you are not looking for FF miles on KLM/AF, then there is no need in for an AMEX.

In the Netherlands AMEX is accepted, but not as good as Visa / Mastercard.

However, if you are planning on flying a lot on AF/KLM/Skyteam, the benefit is that the status you acclaim will be extended to your wife as well.

Are you planning on travelling a lot, or using your card in NL?

There are a lot of options