Frankly, the way a harp is built (model, amount and kind of strings, craftmanship etc.), is way more important than the kind of wood it is built of.
Also, Salvi, L&H, Camac and other big harp manufacturers simply use different wood color finishes, e.g a Camac harp in cherry only has a cherry colored finish.
Several small builders do use different kinds of wood for the body of the harp, like Dusty Strings.
As to the question of cherry vs walnut, in theory walnut is a tiny bit warmer than cherry, but this depends on the tree and even the branch of the tree the harp is made of, as each piece of wood has its own, unique sound characteristics.
So, try the harps you feel attracted to, before you buy.
In that case, you could call the shop and have them play several models of your liking over Zoom or the telephone. In that case you have at least a bit of comparison between the actual harps in the showroom (even two the harps of the same model and wood can sound quite different, one you may love and one you are indifferent to).
Dusty Strings has a web page that talks about the sound quality of different woods; in my experience their descriptions is very accurate! https://manufacturing.dustystrings.com/blog/when-does-wood-choice-harps-matter It does come down to personal preference at the end of the day. When I was harp shopping, I knew I wouldn’t be able to try one out because there isn’t really harp show rooms where I live. I first narrowed my decisions to brands that I can reasonably obtain in my area, and then from where I check out the sound samples of different models on YouTube to help me finalize my decision. The sound sample really is just a sample, and it’s difficult to say how good the recordings were made. I looked around for multiple of sound samples for the same harp in order to get a good enough idea of the sound.