Are Japanese SHM-CD pressings worth the price difference?

No.

I have had mixed results with Japanese pressings, but in general I would say that they do tend to be superior to the originals. I have had more limited experience with XRCDs, but have found them to be outstanding.

If you like jazz, the Blue Note series is superb. Try Hank Mobley: Soul Station

Slight difference.   The cd laser reads the shm cd easier. 
  Now that I’m older, I try to buy important cd releases from Japan, they keep the value, and a lot of them go up on price, so if you sell them later with all things included, obi strip, booklets, stickers/guitar picks, etc etc. 
you will get your money back plus more. 
 The Japanese music industry is far superior to the cheaply made USA lp,cd, etc. 
especially the Japanese LP, far superior.
  I do like the shm cd, never had any skips!

Buy a few of your absolute favorites or must haves to evaluate.  All systems are different as are our ears. Very detailed and transparent systems will notice the increase in resolution and dynamics.  YMMV.

Got to admit I am surprised by the responses. After reading the title, I expected many to splash praise on SHMs; a number of them I've got sound better than not only redbook domestic (USA) versions, but they also crush some over-hyped high-res versions.
As @tom6897 stated, could be system dependent and YMMV, but I have a number of friends with very high end systems and this is one of those rare musical topics on which we all agree! Cheers,
Spencer