I'll add in another pickle.

If you want that deep chatoyance in the wood (I did it again), which is so striking, you really can't use stain or dye on the wood.
Chatoyance is a loaner from the world of jewelry and refers to how the light is reflected deeper in the grain of the wood due to varying differences in the density of the fiber structure within. When something has a lot of chatoyance, you can hold it in your hands and move it around, and the light will get caught in there and reflect as you move it, giving the appearance of depth and movement in the grain.
Rosewood can have a lot of lovely chatoyance, and so can walnut. Roasting walnut increases the chatoyance and makes is a bit more eye catching. Stains and dyes really reduce the effect and make the overall piece seem visually "flatter". The trick is, they can really enhance the grain and make it very striking, so it has it's own attraction. Stains contain much thicker particulate matter whereas dyes are much finer and the particles absorb down further into the wood, so dye can be a better choice to retain chatoyance in the wood.
Walnut is a yellow-brown and rosewood is a red-brown. They can work together and sometimes look nearly the same, but they can also have very different overtones that make them not mesh so nicely. Rosewood also tends to be much darker than walnut and depending on the piece, rosewood can go very dark with finish, almost black. They might look nice together, say a rosewood cap on a walnut body, but you'd really have to have it in front of you and wetting it with white spirits to see how the colour goes together. It's one of those things where if I was doing it, I'd be looking at it under different lighting too - LED, fluoro, sunlight to see how they play together.
Looking at the pics you posted above with the bookmatched rosewood and the roasted ash and walnut (definitely not wenge in that pic), I think the rosewood and walnut wood look great together, though they would not match in visual "darkness".
I also just want to acknowledge the difficulty in your decision. Every time I build a bass, I suffer through this same process.

There are a few of us here with that problem.