wagyu Kobe beef

Yes, you can tell the difference. Value is subjective. To me it's worth it but it's something I would save for rare special occasions.

There are a lot of places that sell Kobe beef that isn't real Kobe beef. Real Kobe beef must be from the Tajima strain of the Japanese Black breed of cartle. It must be born and raised in Hyogo prefecture. It is then graded, with the highest grade being A5. The ‘A’ represents the cow's yield, and the ‘5’ represents the quality of the meat. Top wagyu (Japanese beef) is known for its marbling which can be broken down further. See this Beef Marbling Score chart:

Note the intramuscular fat or marbling in the beef. 

Is American Wagyu worth it?

Is American Wagyu worth it?
American Wagyu is known to be the finest beef in all of America, and although Waygu is graded as USDA Prime, it is certainly the highest on the ladder of all Prime graded beef

What part of the cow is Wagyu?
Sirloin. One of the most popular cuts of wagyu, the loin of the cow offers a rich, full-bodied taste that is truly incomparable. It is often heralded for offering the most characteristic flavours of wagyu, as it boasts the finest qualities associated with this type of Japanese beef

Note how an A5 must have a BMS of at least 8 (ignore the typo on #10).

If you buy the real stuff, the seller should be able to produce a certificate of authenticity. Now take a look at these beautiful pieces of A5 Wagyu (not necessarily Kobe)…

They look nothing like the typical steaks found anywhere outside of Japan. Not surprisingly, A5 Wagyu (again, not necessarily Kobe) isn't cheap. But can you tell the difference beyond cosmetics? Absolutely.

All that marbling makes the beef extremely buttery and rich with a touch of sweetness. It's incredible and among the best and most memorable bites of food I've ever had. But you should know that because of its fatty richness, you can only eat so much and it doesn't really feel quite right as a meal on its own. It's delicate and lacks the beefiness that you get from dry aged steaks you find in western steakhouses. It's a very different approach to beef.

If you can afford it, I would highly recommend trying it. It really is special.