Besides looks I don't see any advantages of alu battery trays, oh and it will act as a heatsink for you lipo's. But in a good geared system lipo's shouldn't get hot.
The "heatsink effect" will only work for part of your pack, umless you're running a 2s or 3s. Having one part of a pack cool and the other hot is not good.
As lipos tend to transmit heat reasonably well, I think a heatsink in there would not be a bad idea. Have some cooling fins milled on the sides (make them sharp too in case some a-hole tries to steal your lipo!) I was thinking of folding and welding some al sheet to make a tray, but kydex is soooooo much easier to work with.