I'm confused... you think there is a lot of scope to cater to niche segments, but then are wondering how to identify those segments?
If you have already identified the segments, then I would just talk to as many people in these segments as possible and ask them what they would like to see. I think that good customer/client dialog is invaluable.
Generally speaking, higher margin businesses are going to be less price sensitive.
There is a lot that comes with being a "dominant brand". In the electronics payments space, a trusted, tried and true product means a lot--moving money around is not the same as picking which site to use to post your blog. I would expect that there is a cost associated with a company moving from one provider to the other. Not only would your technology need to overcome the trust issue, but it would need to be able to validate the cost associated with switching.
Maybe if you spell out some of the segments you are considering, someone could provide more information about that particular segment.