That depends on who is going to use your OS, Jo public or geeks, Jo public useally like a lot of graphics and to boot as fast as possible. geeks like a lot of text info.
But heres my 2 cents,
1. if you go with graphics ,do not use graphic images, but draw the graphics on the fly this will keep things small.
2. We all know Google makes it's money from little add images, what about if some one made a great OS that was free, but had a boot image that could be changed from the net, if you could get 100's of 1000's of people to use it, you could make money by selling the advertising this image would bring, each month a differant image, say Pepsi one month, may be Nike the next month.
Why the BIOS co have not done this is beyond me .
Do not forget, you heard it here first