That is an aftermarket dump valve, it won't make any difference by itself but at least it won't leak like a lot of the original ones do. I know that car had a dual port wastegate when the owner before last had it but you can't tell for definate until you look underneath the car. It certainly has a non standard hose coming off the intercooler pipe which probably goes straight down to the wastegate. You should block off this pipe that I have circled green as it could introduce leaks into the system. Its where the original pipe went for the stock wastegate and leads to the cycling valve

Pour water down the sunroof drains and see that they all empty underneath the car. If one doesnt then it has probably come detached inside the roof trim and is the cause of your damp footwell
.
There should be a tube behind the filler cap drain. If it is missing then it can allow water to run into your sills and eventually cause rust!
That sensor under the handbrake is simply a switch for the dashboard. If the light comes on all the time then the switch is broken. I'm sure a new switch will be a couple of quid only
Bonnet badges are around £20 from Porsche, as is a new key head
Try the latest JVC head units. They have 100's of different colours built in. I set mine for the same orange as the dash clock (and my kids/wife change it to pink when I'm not looking

). It was only around 90 quid and you can plug in an Ipod or USB stick to play MP3's