DEC is an in-game currency that i'm also having a challenging time with. Starts off and feels like it is nothing or only an in-game currency, and nothing else.
But it's an actual currency. It's convoluted but anyone can transfer out DEC into their steem-engine wallet, then exchange that into STEEMP, which you can then convert into STEEM via the in-built Privex market service. It has a fee (it's 1% of conversion, used to be higher than 1%?)
There's plenty that could be done, maybe drop the price of items in the store if paid by DEC (in turn making the developers & owners of Splinterlands more invested in it). New items too.
I would like to see more market activity for the actual NFT cards but maybe there has been some dilution of the market via opensea and its ETH based markets.
tl;dr
dunno
Through @leodex the withdrawal fee is only 0.35%