I believe its has both good and bad effects. Good because such institutions would be putting up their investment in bitcoins which means they also knew that there is a big opportunity to earn from it. While on the other hand it would be risky too because there is a possibility of monopolizing the current market due to its high demand in the market.
This is really why we need bitcoin to be more of a usable currency than just a speculative asset as that would give them more chance to take hold of the market strongly and be able to control it however they wish and like. These are guys who have been living their lives manipulating the fiat system, what makes us think the same will not happen in this scenario with bitcoin. I am still sure what we are experiencing right now is institutional played, so the answer to the OP's question is glaring from what we are seeing in the market presently.
I wonder why this was not attended to since December. Even though your's was post busting, it is good this is brought up. I have asked myself this question several times and to me, I just end up seeing room for pretty much manipulation. Unfortunately, a lot of people are panicking and giving them the chance to be able to have more hold in the market, but I am not sure if this would really mean much in the long run on the amount they are going to be sitting on. I am sure they are having this moment already and we can see how that is leading us. At the end, I only see bitcoin ending up as a store of value with the look of things.
To make Bitcoin more usable as currency there should be a decent solution for scalabity issues. Also, high volatility doesn't help, and as a decentralized currency, volatility is part of its nature, there isn't much to do about it... Bitcoin goes through the store of value path, with some people using it as currency, but not the mass, not the most part of investors and enthusiasts.
I agree with you, the market's movements smell like manipulation, trying to make little fishes drop their coins, so the whales can take all of it and save for themselves, reaching to OP's possibility, to dump large quantities of coins later, a kind of sabotage. So the institutions come with their own Crypto-Currency (centralized one), saying: "Well, as Bitcoin failed, now you can use this one, it's much better, there are a lot of advantages, join us!".
So I don't think institutions investing hard is positive for Crypto world, especially for Bitcoin, but there is nothing we can do about it, it's a free world.