The Risky Woods method is overkill in your case as if you are restricting the game to AGA machines then you can use 64 bit wide sprites. All copper DMA time was used in Risky Woods just to reposition the 8 sprites to get 64 pixels repeating! Hence the bland palette as there was no time to do palette changes.
I thought one of the Dizzy games used 8 attached AGA sprites as a background, repeating the first one at the right edge to give a full 320 pixel wide background layer, but maybe I'm thinking of another game. I don't believe you can change the graphics data on the fly like you can with OCS/ECS sprites, but I don't think you need to. I'd just have a smaller repeating section.
You should gain a fair bit of speed having less bitplanes too.
The other trick you could do is scroll the screen at 50 frames per second but only update the characters at 25 frames. If you're scrolling 2 pixels between one update and the next, move the characters by 2 pixels when they are updated, but scroll the screen 1 pixel for 2 frames. That'll make it look silky smooth!
Hopefully Blitz Basic allows you to do some of these tricks...