Welcome to the boxster world!
The IMS bearing, for whatever reason, seems to be more prone to low mileage cars. Generally I tell people to wait til they need a clutch. However; Since that could be anywhere from 60-100k miles from now, (Depending on how hard you are on it) you may want to replace it earlier. The last thing you want is an engine failure!
You can always have the IMS Guardian installed. This may save your motor, but if you plan on doing the bearing anyways, IMHO the guardian is a waste of money.
As for over filling your car with engine oil. Being slightly over isn't going to hurt anything. Being extremely full can cause problems, but as you describe it there is no need for concern. There is something called blow-by (as I've always, and always heard it referred to as), which is basically oil getting into the intake at WoT or in heavy cornerning (or both), due to slightly overfull oil level. Honestly, no reason for concern.
Hopefully you're as happy as I was when i got my S!!
Happy Boxstering and feel free to ask anymore questions!
Brad