I could type up a novel quoting all the things you bring up. The sit n go format is a great idea and one that should be implemented to the Splinterlands lobby. It will ensure there's always a game to play.
I was unaware of Dgamemarket adding DEC as a payment option. That's something that is note worthy and I hope the Splinterlands team announce it on their blog (if they haven't already).
I would love to see other tournament formats. I don't think adding new cards is needed to keep players interested. Adding a turbo format and getting behind it with some advertising would spice things up for a little while. Then introduce another game format once the excitment for that dies down as a way to keep the excitment going. There's allot of room for all sorts of different tournament structures.
Good points about the introduction of the USD for Potions. I never thougth about the impact it would have on DEC. I'm willing to bet that very thing is the main culprit for low DEC prices.
As for the point about booster not being worth the $2 spend on them, for the most part all boosters have been like that. Booster are simply a lotto ticket to try and hit a $100 + card for $2 with the expectation of flipping cards not worth the original money spent.
Overall I think the devs and team are doing great. They have many working parts and opinions to take into consideration.
Thanks for linking me this topic @felipejoys.
Edit: I think adding a booster to the purchase of a Starter Set would be a good idea. It gives something back to the player that has value instead of just phantom cards.