Because it's a 2006 model I'd suspect one of the following (in order):
1) Vac hoses. Very common problem - they split, crack, or harden on the connections (especially on the actuator because of the heat. Check if the actuator is working, and for a $20 investment you could be on your way again. There's a little rod (10mm thick) underneath the actuator that should move 3-5mm while the engine is idling.
2) Boost leak. Very common and surprisingly easy to spot if you don't have a catch can - just look for the black oil marks near the charge air hose. Splits or cracks in this hose will cause the high pressure air to rush out (perhaps audibly too, as a squeal). Overtightened clamps will pinch the hoses. If you're removing the hose to inspect it, wipe the inside of the hose and the pipe it came off with alcohol to make sure it's clean and dry before reinstalling it. Inspecting the intercooler for damage is also valuable.
3) Vac solenoid, reasonably common problem. This guy is mounted on the intercooler intake. Check the electrical connection first, then make sure it's getting battery voltage on it. If your vac hoses are good, joining the input and output vac hoses together from the solenoid will make the turbo actuator move fully - and if that does, and the solenoid isn't doing the job, it's the solenoid that's busted. Nissan dealers should have a decent stock.
4) Faulty brake booster. Not very common, but it's happened. You'll notice this if the brakes are not working like they used to. To be extra sure, clamp the vac line to the brake booster and see if the turbo actuator is moving at idle. If it is, the brake booster needs attention.
5) Failed vac pump. Quite uncommon and a nasty item to replace, you should consider replacing the timing chains with a double row set from yd25.com.au while you're at it (because one of the timing chains has to come out to replace the vac pump). Again, you'd notice it by the poor braking performance, but clamping the line in 4) won't make the actuator start working properly.
6) Heavily blocked intercooler. This isn't all that common (in causing these symptoms) but people have reported that their intercoolers have been absolutely full of gunk. Remove from the car, pour in half a litre of unleaded, swish around, drain, repeat until the petrol coming out looks like the petrol going in. Leave to stand in open air for half an hour so the inside mostly dries then reinstall.
Usually a lack of boost like this is accompanied by clouds of black smoke. How's yours?