I would be totally against post value capping, for many of the reasons you mention. I'm not sure if this is actually viable or not, but as a minnow who is still trying to break through the challenge of low visibility and therefore low numbers of valuable upvotes, one tweak I would propose is to allocate a certain amount of the Steem being produced to be a kind of base pay for content posted. It would not be huge, but it would be guaranteed. So you know going in that if you post something here, you will get some kind of small reward. Then if your post is popular with the whales, you get the additional rewards, kind of like a commission, and that's where the real wealth potential is.
Having proposed this, I am aware that implementation would come with lots of challenges around keeping fraud and plain junk down to a minimum. I have some ideas for addressing this, but that would make for a much longer comment.
Ultimately no system is going to be perfect or please everyone, so you really have to pick your system and stick with it, maybe tweaking it a little here and a little there. People will adapt and make the most of just about any type of reward arrangement provided it's consistent. Under the current system, people (myself included) are largely trying to boost their potential profitability by networking and gaining followers who will at least see their content in their feeds. Most of my current followers are probably also minnows, but that is OK, because today's minnows will be tomorrow's whales, so it's money in the bank.
I like the idea of making Steemit more fun by gamification. You could potentially reserve some Steem Power rewards for people who successfully complete "missions" that would also serve to educate them about your vision for Steemit.
I think there's a lot of potential here, and a lot of creativity. In making tweaks to improve things, please keep in mind that what we have now is already amazing.
I like your idea, but I think it will attract a lot of spammers posting anything for a small reward.
I see a lot of good articles with 20 or 30 upvotes making only $0.02 or so. If a whale hasn't voted the author isn't making much. These authors might get disappointed and leave. According to steemwhales.com the top 1% hold 91% of all Steem Power. I think this is a problem.
If the reward from a whale vote would be lower and the reward from a minnow vote be higher the reward distribution would be more fair in my oppinion.
You are absolutely right about the spam posting, which is why I say that would be a challenge with implementation. I wouldn't recommend even trying it without thoroughly thinking through how spam posters will be addressed. It would probably require more of an application process for new users, among other things.
I've thought about how narrowing the disparity in value between minnow votes and whale votes might help the distribution situation. On the other hand, the fact that all that whale influence can be bought just as easily as earned is in and of itself a form of leveling the playing field. Theoretically I could become a whale whose upvote is highly coveted and sought after in the next hour by simply buying up several hundred thousand STEEM and then powering it up. Voila, instant whale. The reality for me (and lots of others) is that of course I don't have the kind of money it would take to do that. However, there is nothing stopping me from putting a little bit at a time towards that goal. I right now have a Bitcoin faucet pointing towards my Steem Power conversion address, and I send other BTC to that address as I can. In other words, that's a process I can control and which is guaranteed to work (provided Steemit continues as a viable project for the long haul), whereas getting a large prize on my content is more of a random thing that I really can't control.
My point is the fact that Steem Power (and with it, influence) can be bought actually makes it accessible to everyone. Sure, not everyone can buy a bunch of influence all at once, but everyone who can afford their own computer and Internet connection can surely find a few dollars a week that can be put towards buying Steem Power (or any other "investment" for that matter). Related to that, those 15 cent posts and comments, while not individually impressive, do add up. If I can manage to get three of my comments upvoted to 10 cents each day, then that's an additional few dollars a week going towards my transformation from minnow to whale. This is something every minnow can do. Where in the fiat world do you get this kind of opportunity to actually buy power with pennies?