How would these second layer solutions add value to an existing coin? As bitcoin grows the number of users skyrockets. It's an exponential curve. The blockchain itself can not hope to take on all these new transactions in such a short time. Second layer solutions help ease that burden and allow fees to stay low. This adds value by allowing more and more users to continue to transact and see the coin as a usable tool. It also adds value by giving users tailored solutions like smart contracts when they are needed for particular situations. Second layer solutions keep coins fungible and helps keep liquidity up. As long as people know they can transact quickly and securely trust in the network grows and the coin does well. Atomic swaps add value by removing the immediate need for exchanges and the transaction fees they bring. Without a central point of authority like a crypto exchange, where the exchange holds your keys, you control what happens with your coins and your wallet with atomic swaps. This is a very valuable solution seeing as so many exchanges have popped up to solve the problem of customers wanting to trade one coin for another.
Besides the value it adds, there are some who claim that second layer solutions, like the lightning network, are scams attempting to take the user away from the security of the blockchain. I do not see them in this light. While it is possible for lightning network nodes (computers running the lightning network) to consolidate over time this is also true of mining nodes (computers recording the blockchain). I see these second layers as a reaction to slow transaction speeds, high fees, and miner consolidation. If anything, it allows for more than one solution to pop up and be used on the same coin, adding value to that coin, and allowing it to grow. There are others who claim that if you use a second layer solution you have no control over your funds. This couldn't be any further from the truth, and in most cases, this stems from a misunderstanding of how the network operates.