Here are my thoughts:
I highly doubt a small, niche publishing house is going to rustle up many more readers than you're already getting through Amazon and your website. Some authors think traditional publishers are going to get them a ton of extra sales, but that's often not the case (they especially won't get you 10x the sales to offset the worse royalties). You're already in a better position than many authors to get sales yourself. You don't need a publisher in that regard.
In this day and age I think the credibility bump of being "chosen" and "approved of" by a traditional publisher, let alone a super small one, is overrated. Self-publishing isn't as cheesy and low-rent as it used to be. You can self publish and seem credible if a) you know what you're talking about and write good stuff, and b) you produce your book well (e.g., professional editing and formatting, non-cheap-looking cover, not 100 pages and priced at $2.99). Most customers won't be able to tell the difference, or care.
On the other hand, one thing traditional publishers are better at is getting books into bookstores. That may be important to you, though it's hard to say how many sales that will get you. Though the publisher may not have enough sway / your book may be too niche to actually get any of that rare, precious self space...
Ask yourself what you hope to gain from the supposed increased credibility of being traditionally published. Do you want to use it to feed it back into more books sales or more money? Do you want more clients or speaking gigs? Do you want your information to reach more people? Does having a book be traditionally published as opposed to self-published really move you towards those goals? Does the publisher add anything you can't do on your own? More generally, what are your ultimate goals, and how does your book play into that? To be a famous millionaire self-help guru? To just to have a low-key, but busy, private practice working with social skills clients?