it only discourages it by virtue of the lack of 'investor interest' by taking that approach.
Correct. I think incentiving people down the "investor interest" route is the best approach.
I'm not wholly against individuals having multiple accounts. I just think people should be incentived against it. Right now the opposite is the case and it's proving detrimental to the platform.
threshold system is also a needless barrier to entry
I don't see the threshold as a barrier to entry. People can still purchase SP and curate at any level. I'd argue the lack of a threshold acts as a barrier to those wishing to purchase modest amounts of SP as their upvotes have little or no power.
It means that people of all income ranges, from anywhere in the world, can invest in a potentially high return asset.
It's worth noting that most POW coins offer nothing in terms of incentives for holding, besides speculation that value might increase in the future. That is still the case with STEEM. Someone can purchase at these prices, hold and hope for the value to increase.
That amount is far too much for most people. Today 250MV is almost $11,000.
I'm not wedded to 250MV, the right threshold could be much less. Also the threshold could decrease as the value and adoption increases... I'd leave that to the general consensus.
An alternative approach would be to separate VESTS into 'Influence Shares' and 'Interest Shares'.
I think there is some merit in this. I would guess that some people are curating badly purely as a means of squeaking out more rewards. If forced to choose between the two they'd remain passive. However I still think this approach is still vulnerable to people "having disproportionate influence", so no further forward on that score.