Just trying to figure out the best way to use HD art in C2, man... That is, retaining image quality, scaling well with camera zooming & multiple resolutions, not wasting memory / bloating project / losing performance, and unison between object types such as sprites, tiled BGs, 9-patches, tilemaps, and 3rd party image plugins.
Everyone says something different or contradicts themselves. Now there's talk of mipmapping power of two textures on export? So there will be discrepancies between preview and final build image quality? Oy...
I learned that long time ago, that construct is the only software i think, where you have to optimize before starting a project. But you could replace graphics later.
In terms of scaling if you scale in two's, for example 1 to 0.64 or 1 to 0.62 or 1 to 0.48 or 1 to 0.50 or 1 to 1.12 etc images will look better then if you would scale to something like 0.65. On the side note, same goes for any form of movement, which also will display sprite better.
I suggested you making game in smaller or small resolution, but with big assets, because it does make a difference in the performance after upscaling using high quality scaling, and you can use solely sprites. But it is true you would need to stick power of 2 textures, or at least large textures should be sized evenly, so 2,3 or 4 times bigger. Another reason was that it will restrict you from having too many objects on the screen. In reality having more then 100 objects on screen can start bringing performance dips, but also that will mean you have a lot of objects on the layout, so the loading will be longer.
Continuing on resolution, if you can, rather use 960x540 (or half of that )instead of 720, as it is exactly proportional scale of hd and upscaled to full hd looks much better then 720.
But in the end, a lot depends on the game you are making. What I was suggesting is certainly good for action games. If you are making adventure game, then you need to use diverse assets, thought in this case, due to nature of the game, it will not cause any issues.
And remembered another trick to make assets look better, is to set default zoom to slightly bigger or smaller number. This will glue your assets a bit, achieving more of a painting or drawing look.