hardware accel is a double edged sword
it allows for mass transformation and modification of images with little slowdown, and many images to be rendered, aswell as putting much less load on the CPU, but super large images arent easily handled since it has to work with the GPU hardware.
importing images in excess of even 2000+x2000+ wouldn't be a good idea in any case, since your limiting the amount of other stuff you can have, and it swallows up alot of rendering time. your also limiting the number of people who can play your game.
Every rendering method has its own advantages, learn to use them as best you can. in this case, scaling "nebula textures" and placing many sprites instead of a large image would be faster and better.