Option #1: Starter/Cowling
The new starter is $450 but requires the new cowling update as well. I don't have the current draw numbers but Hartzell advertises their X-Drive starters have the lowest inrush and operating current draw of any starter in the industry.
New (2013 Production style) cowling and baffles are $9,000 for parts, paint, labor installed at CC. Field installation is possible but not recommended.
Replacing the cowling/plenum and starter should lighten the airplane up by 4 pounds. (may vary a little depending on what paint scheme)
You do NOT need the new seat base/battery to run the new starter and cowling. Customers and dealers are reporting excellent starting with just the new starter and original battery.
Option #2: Seatbase/Big battery
Stan tells me he charges $600 for the seat base, $150 for the big battery and $600 labor for the mod. Again, this will add about 5 pounds to the empty weight of the plane.
Summary
Two main paths here:
Option #1: Cowling/plenum/starter will give you more cooling margin and a better cranking starter while lightening the airplane up by around 4 pounds. Also, it will update the look of the plane to be the same as current 2013 models.
Option #2: Seatbase mod with PC680 will give more battery for cranking but ADD about 5 pounds to the airplane. Cheaper in the long run but doesn't have as many pluses.
Bottom line, I would recommend the new cowling/starter.