One thought - even though your product isn't niche, you can market it as though it were. Eg, instead of "a plugin for websites" you're selling "a [solution] for small accounting firms with their own website".

I face a comparable problem (I'm a business coach, which means my clients are pretty well any business). Especially for professional services, talking the talk and appearing more specialised than you actually are (as long as you can actually back it up) helps open more doors.