yeah you got a variable turbo means it adjust itself to spool up faster and for longer so basically it is a combination of a small and a bigger turbo all in one... the VNT mechanism is what does the trick... long story short the reason why we all block the EGR's is because they are the main reason for the VNT mechanism to get stuck, not weird if you think about it... exhaust gasses ( and with that soot particles, actually it's carbon particles, the black stuff that flies out of the rear back-box) get's partly put back into the engine... this and the crank-ventilation ( hot air with oil mist) not only saps away power but dirties up the intake and after a few years of driving it creates a buildup of a tar like gummy substance... this is what cause the intake and turbo's VNT mechanism to get stuck... ( and the head also get's a good old dose of dirty gummy tar buildup too... now back to why we reacted like that... if you know the above than you can easily see why the vacuum operated valves (n75, n249 and n18) could easily be mistaken as the problem while there is something else that is the culprit.
also next-time you have them diagnose the car always ask for the fault codes and a printout of the results... than go home and check it either on here or use google to check the codes and find what it means and a possible solution.
yes they told you the intake needs cleaning... they are probably right
yes the egr is filthy so it will need cleaning ( or even better clean and block it so you never have to clean it again)
yes the VNT mechanism is probably stuck ( and probably the cause of the problem) - yes it needs cleaning
yes it might be a fault N75 valve... but the chances of that are slim, but can't be ruled out without proper diagnostics
also just replacing parts to sort out a problem will get expensive really quick! so find the source of the problem and sort it out.