If your current turbo is stuffed, yes it will be worth it as u don't really have another option other than brand new Nissan or roll the dice with second hand (not advisable in a stag, due to difficult access for removal). I would suggest the smallest possible high flow. That should work well with stock setup. It will be a little laggier but that's the way it goes. Before you do anything, get a proper diagnosis. You don't want to be waisting money on things that aren't required. If it is indeed your wastegate stuck open, that will be the issue of no boost and the turbo itself is probably fine. I had a similar issue on a different car and it wouldn't make boost until 5k rpm. Fixed the waste gate issue and was boosting perfectly again. Good luck.