Without wasting your time, I will go directly to the point..
Auto voting / Curation bots
Upvoting a post without reading just doesn't make sense, it is as simple as that, and no argument can justify it.
Steemit is about quality content, and maybe there are some authors whose every post is worth your upvote (which too doesn't makes much sense). But it is just completely unfair to the minnows, think about it. They are not even getting a chance to prove themselves.
( Because the votes are going to unread posts, and as your part of curation is being done by a bot, you don't care to read and upvote manually )
As a result of this, the trending page is always filled with posts by whales and there is no way for a high quality post by a minnow to land on the trending page. The latter is the outcome of autovoter tools, vote buying, and self voting. ( There was even a post on trending page which literally just said : " happy thanksgiving to all ", and it earned almost 200$, although i am not gonna disclose the user).
Now, it is not always bad that whales are on trending, many of their posts are good and helpful, but a lot of minnows are also writing quality content which is getting unnoticed.
Bidding accounts can also be fraud sometimes. (like the past case with 
Bidding accounts are a controversial topic, as they can give the much required boost to quality posts by minnows. But, at the same time some useless posts can also be upvoted just by transferring SBD's.
Minnows gets demoralised
Too hard for a minnow to get noticed:
As for minnows, it is very demotivating to see that you spend the whole day in creating a post and it haven't been viewed even 20 times, no need to mention that the money is negligible.
Steemit's original goal should be to become a major player in the social media media market, to which users are attracted due to quality content (and monetary value involved as a bonus), not because users see it as an alternative part time business.
And we may deny it, but most of the new users are joining steemit considering the monetary value only. And once they find out that it is not easy as it sounds to make money on steemit, they quit, and never return back because there was no other reason for involvement.
That's one of the biggest reason for steemit having a lot of new accounts created per month but a very few monthly active users relatively.
These are 6 months old stats i found here : https://steemit.com/steem-stats/@mata/steem-stats-total-vs-active-accounts, but enough for making my point.
This kind of user behaviour is not good for a social media site.
A lot of good posts from minnows aren't reaching the audience as they get lost before even getting any audience.
I was a long time quora user, and quora is actually great for content discovery, you can keep on reading quora posts for hours. This is the user involvement level steemit should aim for. (Although steemit has more similarity to reddit.)
(Talking about me, i switched from quora to steemit as i am a very big decentralisation supporter, and also due to monetary value involved. I believe that steemit will surpass quora and reddit in coming years but a lot of major changes will be required to achieve that milestone)
Idea of Decentralisation
There is one more problem which is less visible from just scratching the surface:
The majority of the users are minnows, but the power is completely concentrated in hands of whales. Although it is a decentralised platform in terms of software development, but internally the power is centralised in hands of some whales and they can control the whole flow of the website. So the basic idea of decentralisation is being violated. Here, changing curation rules and giving a bit more power to other users may be the answer.
Competitions from other platforms:
As the blockchain technology is thriving, a lot of decentralised social media platforms are coming up these days.
Other platforms like "synereo" will be soon in competition with steemit, and if they come up with some nice solutions, the current growth of steemit may be halted. Steemit sure has the first mover advantage, but better technology wins in the long term.
This post is basically meant to be a discussion ground for the current problems on steemit and their possible solutions. You are more than welcome to add your own ideas to any point mentioned here.
Note : I mean no disrespect to anyone mentioned in this post
Let's hope that this post does not get lost in the ocean of other posts and it actually gets a few readers.