This is uniquely suited for your style. You basically have pre-made characters that you place in various positions on the gradient background with some though/text balloons. What if ... you just had the two or three gradients you use, and two images per character. (One facing each direction.)
Each strip would be a couple of gradient files (very small) as a table background, and some blank images between the character images to space them out properly. Then have the text in a row above or below the strip. Theoretically, if the images are cached, there would be very little but the html downloaded for each page.
It would be interesting to see how much of your traffic comes from people scouring the archives vs. just checking the new page.
I honestly don't know how much effort this would take to pull off, or how much difference it could eventually make, but it might be worth investigating.