horror

If there are streaks in glass then the factory ‘Water-repellant’ coating the side windows were treated with is presumably compromised.

The coating to the side windows was highlighted by Porsche in their sales booklets. Have others seen commentary on exactly what coating was used, its maintenance or its replacement. Does a handy little bottle of something with a Porsche part number exist at a suitably reassuring price?

The rear shoes hold the when parked, they aren’t used for slowing the car. If properly adjusted/ nothing broken they shouldn’t wear. 
All of which doesn’t really help pinpoint the issue, as suggested above, remove the disc to see what’s actually happened.

From the small print in the  987.2 Technical Appraisal by Porsche when the cars were first introduced:

. . “Air cleaner
All new Boxster and Cayman models are fitted with the same air cleaner as their previous models.
On the Boxster models only, the size and position of the opening to the Helmholz resonator (H) have been modified at the air cleaner output in the intake area for the intake system. This improves the intake noise, in particular on the "open" Boxster models with minimal intrinsic insulation from the roof construction or when driving with the top down” . . . 

And their you have it for 987.2 models: Caymans are more powerful than Boxsters, Boxsters are noisier than Caymans,

Whilst it seems counter intuitive, if the car pulls to the left, it’s probably isn’t the left (NS) calliper grabbing it’s more likely to be the right (OS) calliper NOT grabbing. Try a brake bleed on both OS bleed nipples to flush out any micro bubbles.

As fittings: Jubilee (worm drive) and the spring clamps perform different functions.

A Jubilee Clip is a constant torque clamp: if (say) a radiator hose expands and contacts with heat, the Jubilee Clip stays at the same physical size so it’s actual clamping force varies. The Jubilee Clip if checked after use will often appear to need subsequent tightening, followed potentially by over tightening. Not so much a problem with older engines with cast iron, copper or aluminium outlets but not good with plastics.

The common types of spring clips are “constant tension band clamps: and will move, i.e expand and and contract with heat cycles, maintaining a constant clamping force. Factory/OEM will (often) specify different ‘strengths’ of clip for different applications, with (say) oil cooler lines being stronger than water hose or vacuum lines. Different OEM part numbers for the same sized clamp can be the only way to distinguish one from another.
 

As an alternative view, I’ll put a flame suit on and say, how about ‘NO’.

To achieve greater flow - filtration is sacrificed: more air = bigger holes to let bigger lumps through. 

All my opinion (and what do I know) but if a ‘performance’ filter was so easy why would Porsche or any other manufacturer chose to hobble their cars by not using one. 

2010 car, courtesy of the strange pricing on a awful lot of second hand cars, the current prices being asked are in excess of what I paid 5 years. Insurance renewal a week back, the letter from the broker advised checking values to avoid the car being undervalued in the event of a claim.

How would a RTI work then? 

Canvey Island. I’ve used these people a couple of times to have wheels powder coated. I’ve had no issues, quick turnaround and remount/remount tyres if you need it. 
https://www.jppolishing.co.uk/