I think for agencies as far as how we appear in organic search ourselves, we are definitely going to need to leverage all 3 of the solutions you talk about and agencies who haven't branded their products/services are going to have to do that and are going to have to also employ branding strategies. In addition, we have to optimize for other search ares like you say in your point #2 and we must look at optimizing existing content for voice search and answers/featured snippets like you say in point #3.
Paid search advertising costs money, which at first may seem like a disadvantage, but these costs can easily be managed. With cost-per-click (CPC) or cost-per-thousand-impressions (CPM) campaigns, you spend as much or as little as you want. You can adjust your campaign budget at anytime, so if your business is going well, you can spend a little extra to drive traffic to your website and catch the attention of new customers.
Go to local events or Meetup events and connect with bloggers in your industry. An example of an event I run to connect with bloggers and people in the online marketing word is: http://www.meetup.com/Online-Marketing-Sydney/. Make friends first and then try to gain guest posts later. I am not really a fan of websites which are flooded with guest posts one after another; it is the type of thing which Google is just waiting to target.
BrightEdge research supports that a blended approach is best for delivering high performing content. Not only will combining organic and paid search increase website traffic, but it will offer a bigger return on the investment. Take Retail, Technology and Hospitality industries, for example — organic and paid search combined make up more than two-thirds of their total revenue.