It may be worth passing up the command for a "career" airline that you really want to work for and will stay at long term. Otherwise take the upgrade, get 1500 - 2000 hours in the left seat and then look around.
One of the employment agencies told me "Contracting is for Captains". Some airlines will never upgrade expats and you may be replaced at any time by a local f/o straight from training, experienced skippers are much harder to replace.
Financially you will be on 50 - 100% more money which is considerable when multiplied by a number of years. Also some companies don't treat the f/os too well.
Also you are much more employable as you can work in either seat.
A serious global crisis may delay your opportunity for upgrade for years if you turn this down.