Hi @AdamLPW
Great questions! Thank you for bringing them up.
How do you provide relevant content for a saturated, boring, niche market?
While it may be boring to most, there will still a small set of people that find it interesting (or at the very least need information about it). When planning your content strategy, think about all of the potential questions that your users may be asking as it relates to your service. Start by answering those questions. If those topics are already very saturated as you mentioned, think about the relatable topics/questions that your users might be looking for, even if not directly related to your solution. It shouldn’t be too far off-topic, but if you can provide valuable information just outside of the box, try that.
Also on the saturation issue, that can be more difficult. Our general approach is to first find the gaps; where is the space missing content.
The other approach to battle saturation is to do it better or differently. If your competitors are writing text blogs, make videos. If they’re writing OK content, write great content. I know…easier said than done. 
How do you market a premium product in the above market, when cheaper alternatives are available?
For top-of-funnel marketing, you probably wouldn’t want to market much differently than the cheaper alternatives. The purpose of awareness content will be to attract a broad audience and then you can start to weed out those that are a good fit for you.
Your middle-of-funnel content should speak more to the premium aspect. Why would someone buy a Rolex vs. a Casio? Think like your customers (or potential customers) and elaborate on those factors. The BEST thing you can do here is to talk to actual buyers. Interview them to find out what matters to them when choosing the premium and find the trends amongst your interviewees.
How do you approach creating buyer personas when your software (due to 2) doesn’t necessarily address a problem or challenge to the buyer?
I would create my buyer personas in the same manner. When creating a persona you want to uncover what really matters for those buyers. You mentioned you are selling a premium product…what is it that makes it premium? In your persona building process, you need to uncover whether or not what you think makes it premium actually matters to the buyers. In the case of the Rolex vs. Casio: both watches still time, the Casio needs probably needs less maintenance and care, the Casio is cheaper, etc. Yet, there are still people that buy the Rolex and they have their reasons. Your goal is to understand those reasons inside and out!
I hope this helps!
Josh