I like the first half of the idea, which is to buy HBD in order to get 20% interest.
Here is an idea for what to do with the interest.
Buy SPS to be donated to Splinterlands for the specific purpose of BOOSTING the amount of SPS being given in rewards to players each day. This will inject value in the ecosystem by using the DAO's interest to directly fuel the rewards given to players. The SPS given this way would be bought from the market first so no extra inflation. It is also 100% sustainable over the long term.
I think that there's enough rewards defined in the whiter paper for battles. It's been open information for years at this point. SPS has a capped supply, while DEC does not.
This would induce more selling pressure on sps and stunt any price appreciation. If you want your sps to gain value, you need demand that comes from actual players and ones that wouldn't just sell it. We have many avenues to boost the amount of sps you recieve now as it stands. The buy and burn of dec creates a feedback loop that once it eventually reaches peg, sps will climb due to demand and burns needed to acquire dec. Inflation of rewards just dilutes the value of them.