thats kinda the problem with this car...
it is (or at least was at some time) a very expensive car. most things that improve the looks of the LS are not really cheap (LSE conversion, wheels, paint/wraps/dips...)
as a side effect, most things that are cheap, also look cheap and do not improve the appearance.
a few things that are not all too expensive that are easy to do would be things like window tint, painting/power coating brake or OEM wheels, color matching any/all chrome like the rear surround, front grill, bumpers... HIDs, debadging, exhaust tips, painting lower bumper trim and side skirts,
a good place to start? if it comes from wally world or autozone, then do bother...