koetsu rosewood signature vs. Blue urushi

Is there a big difference between the Rosewood signature and the Rosewood signature platinum ?

For me, it made a difference, but not a significant one. I believe the difference can be attributed to the platinum magnets. The midrange was a tad better defined, but it is hard to justify the difference in cost. I could only tell the difference with a-b testing. I think if someone switched out the cartridge without me knowing, I would probably not notice it.

is it safe to say that bang for buck, the rosewood signature ?

Yes, if you are buying it new. You will be pleased with it. But that is just for the Koetsu. There are a lot of other cartridges out there that are great and sell for less. For me, it is an adventure. I have lots of different cartridges. My current keepers are the Miyajima Shilabe, the Koetsu RSP, the Koetsu RS, the ZU-DL103R, the Denon 103R, The Shelter 901, the Accuphase AC-2, the Adcom Crosscoil SXC-VDH, The Dynavector Ruby Karat, and the Supex SD-900 MK-IV. I have heard lots of others. They all sound a bit different, but are all enjoyable. A lot has to do with the proper matching of the cartridge with the phono preamp, SUT, and tonearm combination. You can easily have a cartridge that on one setup sounds great and on another sounds not very good. That is why reviews are so hard. If you switch out just the cartridge, then you are comparing which cartridge sounds better in your system. That will be different for each system. The best reviews are when they compare a complete setup. There are a lot of biases on cartridges (or anything else) based on what they are matched with.

I agree Capnbob wholeheartedly.
Even when using different phono stage, the sound can vary from cart to cart, etc.
Wow, quite a bit of collection.
How do you compare the Shilabe & the Koetsu RSP ?
I ve heard few times the Shilabe & its quite a cart.