To answer the original question: These computers are essentially the core of the Mac platform. They were the first hit that got kids interested, often the first computers able to catch kids' attention at all, and LCs and their related Performa models are the actual vast majority of the Mac platform.
Some LC series computers have FPU-less 040 CPUs, but otherwise there wasn't really a "the celeron of its day" in the Mac family. (Worth noting: Celeron processors are pretty amazing today anyway.)
Even the original LC, which did use an 020 CPU on a slower bus than the Mac II is useful in some aspects. Back in the day, I went online with one and used AIM on it, etc. The IIe card is neat, but if I were to have a pile of LCs, I'd probably go for Ethernet cards.
I have an LC520 these days and I like it. It's a little faster than the original LC, but mine only has 5M of RAM in it, which provides a pretty interesting challenge in system 7.
Ultimately: If you're collecting Macs because you want to know what the Mac was about, an LC of some sort is absolutely mandatory. If you're collecting Macs because you want low-rent graphics workstations from the '90s, an LC won't really do it for you, but they're nice systems for writing, games, learning the system in general, testing things, and in a lot of cases, LCs will run all that software, even if slightly slower than a Quadra.