I'll just point out that graphics do not cause strain because they aren't stored on the blockchain. As for size, well, larger posts are strictly more costly than smaller ones, but as you say it doesn't seem to increase the cost significantly. It's possible to tweak the parameters to have size matter more for cost too.
About early votes, there's already something to discourage early votes. There's an early voting penalty and it all reduce your curation by a linear factor. Voting at 0 gives up your curation entirely, and voting at 15 is the cutoff where there's no penalty. And before the fork it would go to the author but now it goes back to the pool.
Ooh. Found something you may be interested in. I'll just drop this here: https://beempy.com/resource_costs
This is interesting, thanks!