A star is... coded.

 So I have a plan for the stars.

There are 124 stars, and using 16x16 tiles would require 103 tiles to contain them. Tiles have no more than 3 stars in them. Tiles will also have their own palette (16 colour entries).

There are 4 blink cycles. Rather than use 4 layers of sprites, I plan to use just one layer, with all stars rendered, and use palette cycling to turn stars on and off. At most, the states of 61 stars change in a blink cycle, though some of them may be on the same tile. So worst case, I need to update 61x3=183 words in the palette map. That should still be pretty insignificant as far as processing time for a frame.

In theory, I can replicate the exact star pattern, colours and behaviour - at least as implemented in MAME.

Just need to finish off writing the code to generate the tile and palette data, and some extra data to assist in optimising the updates.

UPDATE: After revisiting the star generator in MAME, it seems worst case is only 47 stars changing state, which is 47x3=141 words written. So a bit quicker again. Tile generation code next...