Unless you have yet another daily driver? Although I too plan to buy an older 911 turbo someday, I'd look at it as a "toy" car that probably won't be driven often and if one does drive it often, it may be in the shop more often than not.
I'd keep the Volvo unless you have another dependable daily driver because I wouldn't expect that from an older Porsche. The Porsche will also keep your pocketbook very active.