I don't think the Boxster 2.7 model will keep its value as well as the other models. Demand for S, GTS and definitely Spyder will keep those models' values strong.
If you are looking to get maximum price for your car, now would be a good time to sell.
However, the question is who to sell to. The luxury dealers, like Carbon Black Auto, etc may be worth trying.
Sadly, a Porsche out of warranty is a minefield, unless you know a good independent workshop. Even then, parts are not always cheaper.
Are you considering a replacement?