It sounds like your booklet is aimed at intermediate-level builders or designers to help them get their regenerative circuits working better. I'm not sure there is such a large audience of potential paying customers that falls in this category. It might be better for you to expand your material to include beginner level material, so that beginners, who might not even know what a regenerative receiver is, would become interested upon seeing your booklet. Having done some fair amount of writing myself (including commercially published books), I'd say that clarifying the target audience - and competing books or resources - is an important part of commercial publishing. It tends to be more time consuming to write material aimed at beginners (where you must explain, motivate, and justify the subject matter and your treatment of it).
Alternatively, if you want to continue to aim at intermediate/advanced builders, then offer some specific teaser information to explain the value of the information contained therein. For example, have you found a way to do automatic regeneration control? Or reduced frequency shift with regeneration adjustment? Improved dynamic range or strong-signal handling? Reduced noise? Devised a new way to control regeneration, couple the antenna, wind the coil, reduce drift, stabilize the operating point, conserve power, cascade multiple regenerative stages, interface a regen with DSP, etc.? I'm sure there are many, many fascinating things to know about regens (and super-regens) - give the potential reader a hint about what to expect.
Anyway, just some free advice - as they say, it's worth every penny you paid for it.