"By the time these plants would be ready to attempt to bonsai, I should have some experience under my belt."
That's probably the best mind set in approaching seedlings. It's refreshing to see someone who isn't set on making bonsai from them immediately.
"Even if these trees are not suited for bonsai, I would still like to grow them. I guess I'm drawn to plants that seem exotic or unique. I also appreciate the challenge."
There's "challenges" and there's "beating your head against a wall."
By all means growth them if you like them. They are not unique. They--at least Acer griseum--are avoided. There's a difference. If you think yoy're breaking new bonsai ground, think again. I've learned that bonsai people are quite innovative and will try just about anything. Chances are that just about any species of maple you're thinking about has been tried and there is probably a reason that some aren't being used regularly as bonsai stock. It's probably not a question of "exotic", as much as it is "not worth the effort..."
That being said, I have a feeling that the pseudosieboldianum will probably work out. I have been seeking a larger tree of this species to work on for some time, as the fall color on them is quite spectacular. The in-ground specimens I've seen have red/yellow color on one side of the leaf and bright orange on the other. I have yet to run across a sizeable--over 2 inches in diameter-specimen to work on though...