You will need to accumulate at least 25,000 miles to get anything interesting. While it won't hurt to enroll in an FF program, if you don't fly very much, you won't get much. If you don't fly again on the same airline again in 12-18 months your miles will probably expire.

Now, there is a whole different way to approach this. Many, if not most, of the people on this board get most of their miles from credit cards and occasionally other sources. Yes, people get free flights. My wife is flying to Europe next summer - in first class - on a free ticket. (We did have to pay a couple hundred dollars in taxes.) You may get a couple thousand miles on American for your trip; my wife and I each got 100,000 miles on American for opening credit cards earlier this year.

Getting those miles does involve some work - reading and absorbing the information on this board, applying for and managing the credit cards, etc. Just a question of if it's worth it to you to put in the work.