There is no way to get more ascended goods than you can produce via trader (unlike the situation with sentient goods, where some players just parasitize on the market without producing anything). And due to decaying nature of ascended goods it is really poor to hoard - the more you have - the more decays. And if we are talking about ascended goods types balance - yes, you can hunt for rare goods even if you don't need them, but the only profit you can get of it is less time exchanging these goods back for popular ones, but wasting your real time on refreshing the trader just to have an opportunity to get your own goods back faster later (or the ones that are ~same popular as yours) is nonsense.
I'm not telling to not take trades, I just tell to post own trades before doing that. And that can be more beneficial even for you, as you get both notification of your merchant is back + a fresh new trades with the goods you need on the market that you can accept while you are on trader anyway.
You might think it is nonsense, but I don't -- I do think that way, and I can't be the only one. It's very similar to how I treat sentient goods. I even strategically trade sentient goods planning on the decay products to produce crystal and silk because I'm boosted in scrolls. So, I do hoard obsidian and velvet just for the decay products.
I don't have the opportunity to do it now, but at T8, I might, especially if ascended crystal is in demand.
And of course I'm going to use my merchants and pick up trades both, because I have an undesirable boost. I just don't want people with desirable boosts not picking up my trades because they already got enough from posting their own. (Or, equivalently, not getting mine because they need to pick up fewer trades.)
To be clear, I don't want people thinking that picking up a hat trade isn't helpful because picking up my hat trade is helpful to me.
And we can see whether or not posting rare trades helps. I think whether or not it will depends on how imbalanced things are and how effective expiring trades are for getting undesirable goods out of the world. If it's close, then what you're proposing can help. If it isn't, then the excess will just get sucked up by opportunists and you won't see a difference.