Ultimately the answer to how to create a valuable altcoin, aka how to make an altcoin valuable, is almost trivially simple:
Build it a strong "buy side".
To keep it valuable, do not "rug pull" your buy offers out from under it and do not issue more of it than your buy offers are offering to buy.
To ratchet up its value further, take all proceeds gained from folks taking your sell offers and use them to strengthen the buy side.
You need not hassle exchanges to try to convince them to list your coin, you can simply tokenise them yourself, e.g.
on Stellar.
Almost all sites articles etc that mention value of a coin, including many that calculate its "market cap" look at the highest price buy offer that hasn't yet been "taken" or at the last price it traded at; not sure many of them do volume-averaging on those figures e.g. average last X number of trades or Y volume of trades or maybe even whether all the buy offers down all the way to the lowest possible price are enough to buy all outstanding coins.
Remember, money is IOUs. They are only valuable if folks know or I suppose even imagine that you are going to "honour" them...
-MarkM-