I don't think DIY is dead at all; I think it's just shifting to (for lack of a better term) social building. At least around here, there are a variety of "maker spaces" that thrive on people working together to teach each other new skills. Sometimes they take those skills and build something solo, but very often they wind up collaborating.
The sheer range of available tools may be a factor now, too. Laser cutters, 3D printers, CNC routers, and all those cool electronic components (including arduinos) that let you build interesting things. If you have the same percentage of the population interested in DIY, but all those other interesting things to play with, then of course some of them are never going to make it around to grinding and welding - they'll be creating new and different stuff, often in exciting ways. Even for the most avid DIYer, there's only a finite amount of time to spend on projects.
In terms of AZ itself, I wonder if borrowing a page from the open software world might be a good idea - pick a couple of fairly popular plans, and make them available for free. You could do it under one of the licenses that allows people to redistribute, but requires they keep the page that credits and links to AZ. So every time they share a plan, it leads back here.
That would give anyone new to AZ an opportunity to read the plans and get a sense for the high quality and level of detail they provide. It also makes it possible to take them back to their friends and maker spaces and say "hey, let's make some of these together". And at those spaces, they'll be able to find help to guide them with the parts of the build they aren't confident of, such as welding thin wall tube, or machining a hub flange. It's much easier to get people to take a bunch of small steps than one large leap.
In the meantime, you could still charge for the rest of the plans. Lots of people are going to want to customize their builds once they get a taste of what's possible, and knowing there are plans out there for those tweaks (and of a quality they are already familiar with through the free plans) may make them more likely to spring for a package. I'd play that aspect of things up, with a prominent reference guide of what unique features each plan contains - such as rim brakes vs disc brakes, the direct steering of a Streetfox vs. the linkage steering of a Warrior, etc.