Density is kinda relative, compared to what BX boards take, you've got high density RAM at present. However, finding lower density 512MB sticks that also run at PC133 may be hard.
There are supposed to be mild performance gains in sticking with the lowest density possible, but that tends to only be practical in "mid range" RAM loadouts, rather than when you want/need the fastest standard and the maximum capacity.
The theory is roughly analogized something like... if your RAM chips are warehouses and you've got one little robot in each fetching boxes for you, then you get better performance when you've got 16 robots fetching stuff in 16 smaller warehouses than if you only got 8 robots fetching stuff in 8 bigger warehouses.
edit: that might make it sound like it should be a much huger difference, but the 16WH robots would be fetching 4 boxes at once where the 8WH robots would be fetching 8 boxes at once, but still there's latency from covering twice the "floor area" etc.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.