Yes it is worth it, but depends on your behavior and the amount of work you put into it. This all assumes that you pay you balance in full every month - if not interest charges will immediately wipe out any rewards many times over.

You could go simple and get a single travel card like the Cap One Venture or Barclay arrival that basically pay 2% back that you can redeem for travel purchases. Your $8000/month and the $400 signup bonus will easily give you $2000 in rewards by the end of a year.

You could go bigger and churn travel cards. I got over $1400 in value from a single Club Carlson card signup bonus for four nights in London. I won't apply for a signup bonus card unless I can get $500 from it. I've done eight this year, so I am north of $5000 in value. I also juggle cash back cards to get 6% back on grocery and gift cards, leading to gas points for free gas. That is another $1500 a year or so.

You could go crazy and get into manufactured spending, but that gets much more complicated and risky.

It all depends on the amount of work you put into it. Living overseas could complicate it, but if you are a US Citizen with US accounts you should be able to qualify for many offers with a 700+ FICO. Figure out which cards and signup offers will give you the best rewards and fire off a few applications.