Well yeah but I would generally be running the lightest tire that fits my needs anyway so it's unlikely that I would be able to reduce weight by changing tires...at least not without compromising some other factor. I would say wheels, though whether you consider that cost effective is questionable.

Probably the biggest weight gain in my Bottecchia when I set it up to be comfortable and ridable was in the wheel/tire combination. Since this was a few years ago and nice polished box section clincher rims were extremely hard to come by at the time (no V-O stuff then) I ended up using NOS Rigida AL1622 rims. Those are meduim width and don't have hooked beads so that dictated using at least a 25mm wire bead tire. And since I was having trouble finding 25mm tires that were actually 25mm instead of narrower, I went with 28mm. So while I ended up with a quality wheel and good tires that are representative of what a decent touring or sport-touring style bike might have had at the time, they were also 420g each heavier than the tubulars. Today I would probably use a narrow hooked bead rim that would allow a 23-25mm folding bead tire and save quite a bit of weight. I weighed a set of rims/tires like that and they were only 120g or so heavier than the tubulars.