Thinking more on this, I would say that luxury is not, according to the Gospel, compatible with Christianity. However, we would also need to point out that neither is gossip, lying, pride and a host of other sins. I have often thought that the reason homosexuality is such a vicious target of Christians is that we like to attack and elevate those sins which do not tempt us, which are not a part of our spiritual journey. In doing so, we have a sense of having “arrived” at least on one point.
Perhaps our attack on the wealthy is similar. We who do not ever have to face this challenge find this sin easier to denounce than those closer to home. If we were to look a a wealthy person who is a Christian, one that is overly-luxuriously wealthy, then we can no more judge him for his wealth than we can judge ourselves for our continuing pride, lying, gossip, etc. So while I do say excessive wealth is incompatible with Christianity, it is not incompatible with being a Christian, still on the spiritual pilgrimage.
I am surprised no one addressed the question of how much is too much. I think the idea of a continual conversion bypasses this whole question, as the lifestyle which is excessive changes as we mature in our faith.