A guy I know got pulled over in a turbo civic (he is on his reds and affected by the prohibited vehicle condition) and got a defect for a blow off valve and where his boost gauge was mounted (on the a-pillar) and the cop said have a nice night.
He's got a front mount (hidden by mesh), bov (now moved to under the front bumper so you can't see it), turbo timer, boost gauge etc and thats the only time he's been pulled over.
He's done well to hide things, but either way, he got off lucky with the defects, and he said the cop had his licence and was looking over it.. and it blatantly says CONDITIONS: Y
With the amount of times I've been pulled over for doing nothing wrong, I wouldn't risk it in a turboed car; but then again, if you leave it stock, don't put chromiez, a big spoiler and custom plates on it you should be alright.