Spikey--the problem is that it is more difficult than you think to 'fly for a few years'. Once you give up a seniority number to come here you start at the bottom and, at the moment, command is probably 7 years.
If you decide that the situation is one you want for you and family you are making a huge commitment. It is costly to move and set up house. Going back is costly as well.
The biggest variable for me would be my ability to go home and find suitable work. If your plan is not for the rest of your career you best have a plan on how to back home. I am guessing that if you spend 5 years here your not going back at the top of a seniority list. Will there be airlines hiring at the time? If you have no left seat time where will you slot in? If you are in the left seat is there a DEC position available?
Basically what I'm saying is that the most difficult variable in the decision making process is how to get back. Once you are out it is very difficult to get back- at least without a major paycut or change in lifestyle. The airline biz is fickle and may not correspond with your desire to head home.