I know i'm gonna feel so dirty after posting in this thread again.
Steel doesn't have bad or broken gameplay mechanics, or look out of place, it's a completely viable CP structure that required no modding and had several people in this community, including myself, aiming to produce this effect in exactly the same manner; before we even realised it existed in the form of cp_steel.
I can't remember where i said it but it seemed to get an agreeable response from a lot of the community. So i'll say it again for your benefit: More or less;
a gimmick is something "for funzies", something that is out of place, floating platforms, teleporters, randomly crushing walls, illusinary walls/platforms that you fall through, secret rooms full of health and ammo. A short fall attempt at trying to be different to stand out, or something that's "amusing" so "why not".
I'm pushed 50/50 to calling your map a gimmick. It works. It doesn't really stick out other than the fact that i can't see why red or blu would stick a bomb on a circular track and race each other on it. What pushes it to gimmick for me is the uber speed. Your huds fine. It is just the placement in time/reality, the situation itself that really throws off it's believability.
A gimmick isn't necasserily an under-produced map, it is just a trend that beginner mappers intially take this route in mapping; which isn't necasserily a bad thing as they get to learn the software, engine, and it's capabilities. But that doesn't mean there's any reason to release these to the public. I would admit that several of my first maps could be considered gimmicks; but i never realesed them.. Though to be fair, pretty much anything could be justified in HL1 as long as it was made believable by good brushwork/geometry. If it doesn't work in the real world, make your map based in Xen.
But to your points.
1. I don't really agree that the gimmick drives the beginner mapper, it is just the product of ignorance. (That isn't meant to be offencive, it's just a fact).
2. Because there are many is also not a reason for people to neglect polishing their work; they just can't, they simply don't have this abality yet. They don't have the experience or knowlegde to do so even if they wanted to. A result in the trend of beginner mappers creating gimmick maps.
If a decently experienced mapper decided to produce a gimmick map it would deffinately be pretty should he choose to put the effert in; heck, a lot of the rat maps for TFC were damn impressive. But they were still gimmicks, because they didn't satisfy the criteria of being a TFC map. As loose as the criteria were.
To your third point, beginners don't invest time in their work because they soon realise that it's not the masterpiece they intended to create. They have improved, and move on to something more advanced. Either that or they just don't have the motivation to stick it out; the only alternative solution for these people is to produce a gimmick map, regardless. The only other option is a killbox.
I'm not as much trying to tell you you're wrong, i hate doing that to people because it's pretty damn mean and makes me feel arragont and egotistical. But maybe that would enlighten the situation more.