Recently, someone asked me again whether LST and re-staking are really good or not.

Honestly, the returns are just a few points: the basic rewards from underlying staking + protocol incentives (often just issuing tokens/points) + you taking the LST and doing another layer of lending or market-making elsewhere to earn the spread.
It sounds very promising, but in reality, it all boils down to one thing: someone is paying.

The risks are pretty straightforward: LST itself has discount/liquidity issues, and the additional staking layer is more like "selling the same security multiple times," where problems don't just cause slow losses but can lead to chain reactions on-chain and rapid collapse;
there are also smart contracts, oracles, liquidations, redemption queues... each layer is leveraging more, and I, having been hurt by impermanent loss before, really get anxious.

Recently, social mining and fan tokens seem similar: attention is called "mining," but I always think twice about who ends up paying when the miners finally dig up the rewards.
Anyway, before I join a pool, I first run through the worst-case scenario; if I can't figure it out, I just assume there's no profit...
As for whether you can repeatedly collateralize safely, I also can't say for sure.