I have seen them valves lose 20bhp+ with ease.
You also want to check the PCV system for leaks.
Other things to check are throttle body opening, cam timing, over reading MAF, naf N75 and weak actuator
It get a good picture of whats going on you will need to log blocks 013 and 025. (ebay for a vcds lead)
I would ecpect a good running AGU to make 150-155bhp in stock form, any lower then I would state to look for issues.