Putting off a 4 year old baby tooth filling is no big deal... tooth is not permanent anyway! The 18th birthday gift was time sensitive (the opportunity of a lifetime must be seized in the lifetime of the opportunity)... and that magical age will be some of the best times and memories for your oldest.
I am with you on your decision making process ... but life is never black and white and your wife NEEDS to tear you down to feel better about herself. Understanding the psychological reasons for her bizarre thinking patterns and actions will help you realize that it is not you really... she is just acting out her addiction in a manner that is very normal for an addict. You are on the alcoholic crazy train where everything is like walking through the looking glass.
Coming to this website is like taking the pill in the Matrix... helps you see the truth and the reality! IF only we could all just wake up like Alice and it was all just a bad dream!