Obviously, I agree with your choice ('course the deal did change when you found out it wasn't really an X-51 - something about the original deal didn't sing true to me). I think it makes the most sense.
But, you still have a storage issue right?
If so, don't do anything to the Boxster - you won't get your money back. Instead put it in the 911SC. That money's much more likely to 'grow'.
Plus, you don't have to do it all at once, put it on a 3 yr. plan. In the end, I think you'll be happy with that approach plus, it'll give you something to do and you'll become reacquainted and re-enthused with the SC.
Any parts you need are still available and also do a standing search on ebay, contact LA Porsche, Parts Haven and Okla. Foreign to see if you can save a buck too. Good Luck!