Disconnecting the wastegate line and plugging it does not allow the compressor wheel to spin faster.
What it does do is allow the turbo to build more boost. Your wheel will only spin as fast as the exhuast wheel drives the compressor wheel.
The advantages of disconnecting the wastegate line are faster spool up of the turbo, higher boost, quicker throttle response.
I have had mine disconnected and plugged for over a year, Abobb has had his disconnected for who knows how long. I know there are alot of members on this site that have been running this way for a long time as well. None of us have had any problems because of this line being disconnected and plugged.