... in life, you'll find well-intended but diverging answers to your question.
My recommendation is: Don't change it.
Especially because you've never had any issues with coolant and have only had to top off once.
The coolant system is a closed loop that can only be contaminated from an external source when you have a failure, generally a gasket, pump or cap..
Once you get into changing the coolant, you're opening up the system for possible issues with air bubbles left in the system when refilling which, in my opinion is the biggest culprit of cracked reservoirs.
My personal car is almost 14 years old and has 213,000 miles on it.
It still has the original reservoir.
At 200,000 miles I decided to check the "lifetime" coolant to see what it looked like.
It was clean and clear. I saved it and it looked like I had just mixed a new batch.
I would however, make sure that you have the latest version (04) of the coolant cap. Older versions have been known to leak and let air into the system causing coolant to dump and/or cracking the reservoir.
Happy Boxstering,
Pedro
Pedro Bonilla1998 Boxster 986 - 311,000+ miles:
[www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)
Racecar spelled backwards is Racecar
"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"
"If you wait, all that happens is that you get older"... Mario Andretti
"Being second is to be the first of the ones who lose" ... Ayrton Senna