I too have developed a pretty "serious" Canvas application that people actually use on a large scale, http://www.luckyvoice.com/sing
While I agree with your suggestions (caching is absolutely a must, as is batched rendering etc), but I think the real issue is the lack of good-quality canvas libraries that have the kind of breadth of functionality that their native counterparts have have. All of these "performance hacks" are certainly not unique to canvas, but what is is unique is the developer (user of these APIs) having to care about them. They should be abstracted away.
Libraries like Paper.js (which I've used and extended a lot) and EaselJS are bridging the gap, but they aren't there yet — either because they aren't feature-complete in the way that they need to be, they're buggy, and/or they don't seem to be getting enough community development (or in some cases, want it).
While I agree with your suggestions (caching is absolutely a must, as is batched rendering etc), but I think the real issue is the lack of good-quality canvas libraries that have the kind of breadth of functionality that their native counterparts have have. All of these "performance hacks" are certainly not unique to canvas, but what is is unique is the developer (user of these APIs) having to care about them. They should be abstracted away.
Libraries like Paper.js (which I've used and extended a lot) and EaselJS are bridging the gap, but they aren't there yet — either because they aren't feature-complete in the way that they need to be, they're buggy, and/or they don't seem to be getting enough community development (or in some cases, want it).