I'd say that back in it's day, Dundjinni had a fairly sizeable userbase, despite the fact that it wasn't particularly fast, nor super-easy to get up to speed on. DJ is, sadly, no longer viable to use on modern computers, and nothing much has really come since to replace DJ. My app, if it's to be compared to other mapping apps, probably resembles DJ the most (in concept, not in execution).
CC3 (and CC2 before it) has sold a lot of copies, but I suspect a good percentage of the people who bought it were overwhelmed by its complexity and underwhelmed by its output. Perhaps people who got burned will never invest in another mapping app. That's unfortunate, but there's little I can do about that. I plan to offer a downloadable demo for prospective customers to try the app out and see if it fits their needs and meets their expectations. They'll be able to judge for themselves if it's worth the $25 or $30 investment. For a lot of folks, if the app saves them several hours of grief and frustration, it will have been well worth the (minor) investment. Think of all the people who didn't buy CC3 because of the high cost or the complexity. I think that number is far greater than those who did buy it. And perhaps some of them are waiting for the right app to come along.
I suspect a fair number of people buy Paizo battlemaps, and/or geomorphic map tiles sold by numerous content providers. These people want nice visuals in their games, something to match the minis they've invested in and took the time to paint. But Paizo battlemaps are "set in stone". You can't really customize them much, if at all. And geomorphic map tiles look great, but are a major hassle to put a layout together in Gimp or the like. It can take hours, and isn't particularly fun. So if my app can help serve that market by letting GMs create great layouts in mere minutes (and have a blast doing it), I think it could prove quite popular.
LordEntrails, please don't get hung up on the fact that my app can stitch map tiles together. That's just one of the features, not the only thing it does. It can also be used to populate a generic terrain, as you describe. It will have filter-like effects, so you can draw walls using textures, and the walls can cast a shadow, have beveled edges, etc.