All the ingredients have been mentioned for valuing the extra value of SE for you (upgrades, concierge, extra bonus miles if chosen, instant KK etc). But think about how you value your time...

If it were me, if I usually flew paid-Y and upgrading was a concern, then I would do it, but not as a 3 day mileage run but as a 7 day mini-vacation. If I usually flew paid-J and did not have the time to turn it into a mini vacation, I would not do it. You could just continue calling the concierge (available in paid J but not talked about) and the extra miles would probably be close to covering the mileage run cash cost but not enough to give up 3 days of my free time if I wasn't able to make time to sightsee on the other side.