1. Dogecoin is like a pool. When you buy something use dogecoin, you are pumping water out from the pool. Because these dogecoin will be sold for USD. If no new water(USD) come in, the pool will be smaller and smaller till dry up. You use more dogecoin to buy things, the pool is drying up faster.
The analysis you made on that thread's last few posts are fine, but I want to point out that you gave to much importance to the small problem quoted above.
Buying things with Dogecoins is fine, because that gives an incencitive for merchants to accept it, which gives legitimacy to the Dogecoin economy and thus is positive for the coin's value in the long run. Plus, I doubt there are more than a few million dogecoins spent everyday, and it's safe to say that many of the users buy back their coins after and/or spend them with merchant who keeps their dogecoin (a good number of the sellers on suchlist and other marketplaces do that).
The main problem, really, is the current hyperinflation which encourages multipools, who still are about half of dogecoin's hashrate, to dump more than 60 BTC worth of Dogecoin per day, plus the whales who are dumping since a few weeks (this is proved by the fact that the amount of Dogecoin in the 100 richest addresses dropped considerably).