If the supply of any given good is pre-determined (and both these experiments have a tiny effect on the overall supply of STEEM / SBD)

Neither is tiny (therefore the supply is not per-determined)

Hive account@burnpost, last I saw, was the largest single recipient of rewards and about 8% of all rewards. I don't consider that insignificant. But really the goal of the project isn't to be a particular size, that is up to voters. The goal is to give voters the option to direct rewards to burning, which it does. If voters vote a small amount, or a large amount, or a medium amount, then so be it.

As for Hive account@sbdpotato, it is already reducing the supply of SBD by more (about 500 SBD per day) than the amount being introduced into circulation (about 285 SBD per day), and that rate is growing by about 50 SBD per day. Over time this is very much not insignificant. (Since the SPS proposal is now funded, the rate of increase will be much greater.)

Or to put it another way, if these were really insignificant, they would not show up on Trending and we probably wouldn't be having this discussion. Clearly voters have seen fit to allocate significant rewards to these efforts.

Clearly, price of STEEM has been going down not only due to the increasing supply, but more so because the demand hasn't kept up.

No, it is absolutely both. To claim otherwise is silly. There is an enormous amount of Steem being sent to exchanges and sold every single day and every single week. It absolutely has an effect on the price and has had an effect on the price.

I'm all for increasing demand, but I don't think making a pretty Trending is a signficiant factor in that. We had months and years with all sorts of different Trending pages. The two things that have remained constant are: 1) Everyone is never happy with what is on there. 2) Neither the Trending page itself nor paying rewards as we do to the types of posts we do has demonstrated real effectiveness as a growth driver for Steem, nor a demand driver for STEEM investors.

If you have new ideas how to boost demand (and growth), I'm all ears. In the meantime, I remain firm that giving stakeholder voters the option to vote to reduce supply is a positive and not a negative.

One last thing, for all the 'ugliness' complaints about the visibility of burns and other economic projects on Trending, as an investor, seeing that a good chunk of inflation is going to a burn is more of a positive to me that makes me more likely to want to invest (i.e. increasing demand) than seeing that my investment would be inflated away to pay people for posting a picture of a tree.