I haven't been on in a while, mainly because of work but here's something I whipped up today.

That smooth ass glare from the edge is lovey. Is it just a rounded edge and carefully aligned light or did you do some wizardry?
blockland seems to have been rolling fine for years without them
That's because the majority of models rendered at any given time are bricks and those don't have LODs. (But they could have.) An average server might have 16 player models, 6 vehicle models, maybe 20 item models. Out of those vehicles probably have twice as many triangles as the other two.
Wouldn't it take more resources if the model had more data in it (for the different LODs) than just having a single model to render, despite how high poly it may be?
I'm not sure how LODs work in this game, but for some reason, i'd just assume that if the DTS has more data in it for the various LODs, it'd take up more space than just having data for a single model, but that's probably wrong, yeah?
That is correct. It's only logical. The DTS file would indeed contain more than one model but you need to remember that LOD models are supposed to be lower quality than the actual model. At most I would estimate that LODs would only double the file size.
As far as my programming language goes this doesn't affect rendering performance and the read/write (ghosting) performance would only be affected slightly. Same goes for loading datablocks when joining a server. All things considered LOD models can still boost frame rate quite noticeably (Less so in Blockland though, read above) so if you ask me LODs are certainly worth it.