Do you think it is worth upgrading or buying a new laptop

It depends on your needs! I still have an upgraded Late 2011 system (with a 2012 logic board)! For Web stuff its more than enough! Even writing in Pages and word is not bad. Even gaming and video editing is possible just don't go to hard.

Boosting the systems RAM to 16GB is by far the easiest upgrade. Putting in a 1 or even a 2TB SSD would be the next, but you will need to replace the HD SATA cable as they often need replacing and hard to diagnose when that are failing. Even still its not brain surgery!

The area you will have issues with is Sierra is the highest your system supports without using a shim service to allow you to run needed macOS versions. But be careful Often times Apple loves to break things as such don't let your system run updates or newer macOS's automatically, you'll want to make a good backup then run it.