Okay, so here's your answer.
Google is an octopus with many hands. One hand ranks websites using an algorithm that includes many factors. Google gets to decide what those factors are, and how much weight to put on each of them. G+'s may or may not be one of those factors.
Another hand of Google has created G+ in an effort to establish a product/service similar to Facebook. Google creates and either keeps or gets rid of lots of different products/services, so it's intent with G+ ranges on a scale anywhere from purely experimental and will be gone someday to something that will replace Facebook and run them out of business. Where it falls along that scale is a matter of supposition and guesswork. What we know for certain is that it exists, and that's about it.
So, your question has to do with what one hand of Google intends to do with a product/service that another hand has created. How much "weight" does (and will) Google give to it's own "G+'s". Right now, it's marginal. Minimal. Almost nothing.
One mistake a lot of people make is that they assume a static universe with constant variables. When reading the entrails of "what Google is doing", one should always keep in mind that Google experiments. It's marketing, after all. "A/B testing" and all of that. I've seen variations in the weight certain factors have based on the geographical region (in Local search results), and variations the weight of certain factors across different niches (also in Local search results). I assume organic results will also incorporate the same dynamics.
So the short answer here is "it depends". It depends on internal decisions Google is making (which can change), it depends on geography and it depends on niche, and it probably depends on other factors. My opinion is that, for all of the above, G+'s do not mean much in the general, overall composite, and I would be interested to read anecdotes and opinions that contradict this.
Finally, I'll mention that there are situations in search engine results where Google gives a boost at a particular threshold, and less or nothing after that. Meaning, "0" is nothing, "1" is good and "2" is no better than "1". Or it could be exponential.
0 = 0 units of Google juice
1 = 5 units of Google juice
2 to 10 = 6 units
11 to 100 = 7 units
101 to 1000 = 8 units
1001 to 10,000 = 9 units
etc....
Meaning that, 1 is good, 2 is better, but 3 is not. 11 is better but 50 is not.
All of this to make the point that I believe one should at least get a minimum number of G+'s, but this idea applies equally to any other signal that Google might utilize, such as reviews, facebook likes, backlinks, etc... I would do some research into the top ranked sites in order to get some sense of scale, and then do whatever needs to be done to make your site's profile similar to everyone else's.
One caution I would throw out is to avoid being the niche "leader" in G+'s, or any other factor. The nail that stands up will be hammered down. When Google goes hunting for blackhat practitioners attempting to game their system, they don't focus on the sites that are on page 5 or page 10, they are going to look at the top 3 for "unnatural" anything, to include G+'s (and anything and everything else they can define).
So if, for example, your niche's #1 website has 10 G+'s and the #2 website has 7 G+'s, stupid, reactionary "analysis" might conclude that 20 G+'s would be a good idea.
I say that would be an extraordinarily stupid idea, as the oddball website with 20 G+'s, against the backdrop of an entire field of similar websites that have dramatically less than that is going to underline the fact that someone is gaming the system, and invite Google's wrath. The algorithm is just a dumb computer program, but your competitors have the ability to trigger a manual review, and all contemplation of blackhat methods should always keep that grim reality in mind.