I'm not sure you've understood correctly. In my proposed system, people propose projects and these projects are advertised on the centralnotice banners. When clicked on, readers are taken to the individual project pages and donate to them directly, rather than donating into a central pot.
(a) people put forth their own money, and therefore assume the element of risk themselves.
Not sure what you mean here? Readers will donate their own money to individual projects.
(b) people who participate in crowdfunding do so with highly variable amounts - from a few dollars to several thousands - according to how much interest they have, and that's an important dynamic of the funding process.
Nothing stopping donors donating different amounts directly to projects.
(c) many (most?) of the people who contribute to campaigns of this nature
do so for the perks, or contribute /more/ to the funding because of the perks.
Well, Wikipedia is successfully crowdfunded at the moment without perks. This just breaks it down into individual projects instead of crowdfunding the entire entity in one go. Intuition would suggest that we'd raise more money this way rather than less, because of the variety of campaigns, and the effectiveness of a community at evolving campaign designs over time.
Of course, there's nothing stopping projects from offering perks either. Wikipedia swag perhaps? All the fulfilment logistics are already there via the official shop.