t3K|Mac, you can always make half-size (actually 1/4) duplicates (512*512), load them as non-compressed, and use them for reading the light info. Together with compressed 1K maps you still save 75% VRAM compared to your current situation / non-compressed 1K lightmaps.
[if my calculations are correct: big lightmaps DXTCd are 1/8 of original size, and 512 "dummy" lightmaps are 1/4 of the original size)
[if my calculations are correct: big lightmaps DXTCd are 1/8 of original size, and 512 "dummy" lightmaps are 1/4 of the original size)