People invest in Steem Power because they believe that Steem provides a desirable social function as well as an equitable distribution system for newly issued cryptocurrency.

You are committing a logical fallacy in your question asking why people invest in steem power, as though the only mechanism for distribution is self voting. If you are that much of a bore nobody votes on you, why should the network bear the cost of your spammy self votes and give you money for giving nothing to nobody? The logical fallacy is called False Dichotomy. This is almost the favourite tool of political rhetoric. It is also an attempt to intimidate the querant and assumes they are stupid and don't realise the list of options has omissions.

The thing about not being able to get money out is a non sequitur because we are not targeting accounts with under 1000SP, both because they are mostly new, struggling accounts, and the proportional impact on rewards will be greater (though still miniscule). The votes it gives are absolute minimum and only will rise as an account continues the comment self upvoting. And lastly, it won't flag original posts because this is a default in the user interface and would be unnecessarily confusing. Self voting takes a specific conscious effort to do, and we are aiming to break that habit, and show people how it feels to not lick their balls.

Everyone votes for their friends, usually because they like what they friends do. Usually this is why people become friends.

EDIT: Not only that, but a secondary, positive feature, is that if you have previously self voted comments, and then stop, in a random time period from 2-8 hours, your non-self-voted comments will be upvoted at 1%. This may seem a trifling amount, but the economics of managing the bot's voting power mean that once we get through to a person, we want to at least show them gratitude by incrementing the vote count, even if it does not mean very much, and it saves the bot vote power because every subsequent upvote you make will increase the proportion up to the limit at which it neutralises your reward.

And the bot will not forget your past behaviour, or the level at which you decided to stop, because maybe you arbitrarily vote your comments up. This also accounts for those who don't upvote every comment they make, perhaps because they aren't entirely greedy. To reset it to zero would open up the possibility of gaming our bot, which we will not allow.

The upvotes she gives will continue indefinitely until the bot is decommissioned.

If you are wondering about whether a mass of people with your mistaken ideas about what we are trying to achieve here will attempt to spam up the chain with self votes, then you also, as a collective, will show that you care more about keeping your ability to divert rewards away from those who vote for others, than the community as a whole, which will then invalidate your argument.

And some day in the distant future, when we have full AI bots, people will be able to automate the investigation process to locate sockpuppet accounts. I have been working on simple rule systems for this, but they require intelligence to find sufficient links between the activities of an individual engaging in this activity. It is on my agenda for development of my distributed network architecture design, which I started to do intensively when I went on a holiday from Steem after I got tired of struggling with getting Steemit, Inc to make the HF 19 change. My planned media monetisation system requires this, after the network scales up, and I intend to work on this in parallel with my work as a Witness on Steem, because I, like many others, consider Steemit, Inc. to be an absentee landlord, and just as Dan Larimer has expressed when talking about how he moved on from BTS to Steem, and then to EOS, it was his intention that at some point the community would become the arbiters of who would be developing it, and develop a community governance system to make it more responsive, by opening it up wider, and monetising the code production itself, directly.