Yes the money is amazing but I think you need to set a plan of how long he will stay working away for and set clear goals of what you want to achieve with the money otherwise its very easy to spend it and get no further in front.
This is a very good point, it is easy to get used to an increase in salary and then it makes it so much harder to drop back. DH is currently doing higher duties, and the extra income that he is earning just goes straight onto the mortgage as an extra payment each fortnight. So we are geting the benefit of the extra money, but as we are still paying off the mortgage at the same rate as before, if he drops down a level then the only impact is a slight reduction in payments each month - we don't have to cut back on our lifestyle in any way.