There are a few especially significant lights that are rare and have collectable value but usually this doesn't happen. Buy lights because you like them, not as investments. They're more like a gourmet meal than a painting. This is especially the case with LED flashlights, since LED's are high tech semiconductor devices like microprocessors, that keep increasing in lumens just like microprocessors increase in megahertz. Last year's amazing LED light is like last year's amazing computer: ho-hum by today's standards.
Yes there have been a few lights that uniquely filled a need, so they became valuable when discontinued, until something else came along. The Arc AAA was $25 or so before Arc LLC went out of business. Their value then shot up to $60+. But other comparable lights (Peak Matterhorn) came along, and Arc itself reappeared in a different form and started selling AAA's again, so now the old AAA's are no longer worth nearly so much. Similarly with the Arc LS, while the first run might be collectable, and I guess the ultra-rare LS3 might still command a premium price, the favorite model was the LSH-P and those have declined in value since modern lights are better. The most desirable new unit was the Arc4x at around $300 and that was also ultra-rare (HDS claims only 5 were made) but I think those have dropped in value since the HDS EDC series performs at least as well.