That machine reminds me of a Kawasaki 750 I had at one time.    The death of it was : At 45K-miles the cam chain was stretched too far .   Well , I didn't want to pull the crankshaft out to loop a new chain over it ... so I used it for trade-in .   The Kawasaki also only got 42mpg .    
So
My next question is ... Does the Suzuki cam chain have a master link or is it the ONE-PIECE type chain.  

I've noticed some of the newer Honda motors have the chain on the end of the cam instead of the middle.

The TEMPTER sure is a NICE-LOOKING machine !   I'd like to have a new one of them .  
Your right about the RE-Twin being a modern replacement for it ... maybe the RE sales #'s will spur more machines like it , I hope so.    The Kawasaki W-650 I have is easy to like .   At 440 pounds it's still light enough to be FUN to ride and it gets 55-60 mpg-US gallons.    

From personal experience , I know - weight matters more now than it did twenty years ago.   I see my Harley/G-Wing friends adding a third wheel to their bikes while I get lighter weight machine and run circles around them , heck the Savage has been running circles around them everywhere but the interstate even before their third wheels were added !       

Be careful with the GR650.  A lot of them chewed up starter gears and you can't get the parts to fix them.  

I've nearly pulled the trigger on a couple of them, before realizing I need another project like I need a hole in my head.  haha