I've been active in OSS game and software development forums for about 10 years now, and on the majority of said forums there are people proposing open-source DF projects every 6 months or so. At this point I'm in "I'll believe it when I see it" mode.
I've been on the dev team of a couple of successful OSS projects and a LOT of projects that sounded great on paper, but failed miserably in execution. I'm no Linus Torvalds, but these tips might help you:
1.) Open Source Software is 90% about marketing: Convincing talented individuals to put uncompensated work into your project is magnitudes harder than making a sale. The #1 killer of open source projects, by a landslide, is leadership that is unable to sell other developers on the project's vision. The guy who critiqued your pitch was spot on.
Being the leader of an Open Source project is tough, and there are plenty of world class developers that don't have the people or business skills to pull it off (there's no shame in that). It's an extremely difficult balancing act between herding all the cats in the direction of the project's vision, but still being able to give up enough control to let talented developers make your project their own passion. Remember, a great developer can fork your project at any time and take your community with you.
2.) Consider not starting from scratch: The joy of open-source is that you can fork something similar, and borrow code and assets from a gigantic amount of projects with compatible licenses. Help me understand why you'd spend tons of time recreating the basic groundwork that other open-source DF-likes have created. Goblin Camp, in particular, seems like a great starting point: It's a very inactive project (so you can leverage the fork to attract restless members of the GC community), the code is clean (at least the last time I looked at the source), and it's already geared towards your stated goal (a pared-down DF-like).
On a side note: Goblin Camp's history also provides some great pointers on the pitfalls of open source development. In particular, it generated a huge amount of press and social media coverage, then squandered it by alienating many talented devs that volunteered to help with the project. There's no point in turning your pet project into a community-driven OSS project if you're not willing to compromise and work with contributors.
I really believe that Goblin Camp would've succeeded if the creator had been more willing to accept criticism, code, and assets. I had A LOT of other frustrations with the creator, but I'm not here to hate. Things got better after the Goons stopped dominating the GC IRC, but it was too little, too late.
3.) Put up or shut up: Most talented developers aren't looking to build your project for you; they either want to create their own project, or contribute to a worthy project. The burden of proof is on you when you say that DF's code isn't that complex; if that's the case, then there's no reason you shouldn't have some sort of tech demo to show.
David White attracted a strong dev team in the early days of Battle for Wesnoth by running under the philosophy that people will only participate in a OSS project if they see strong progress, and realistic ways that they can contribute bite-sized amounts of work. He did every part of the first few releases of BfW himself and it was NOT pretty. It did, however, very quickly attract people who looked at the project and said "Wow, this is promising and the dev is really hitting milestones! I see some places I could contribute."
The most famous example of BfW's early success was the artist fmunoz who saw that the concept was solid, and then decided that he could easily contribute vastly superior sprites to replace White's placeholders. Once the graphics overhaul took place, even more developers came on, and the rest is history.
4.) Create a Roadmap: Figure out what you want to accomplish with your project, then create a mission and milestones.
The reason why your statements about elements of the project being fairly easy were met with derision is because this has been said a million times before. I can't even count how many projects that I've seen pitched by guys with no programming experience who named-dropped engines and stated that it would be a cakewalk.
Create some realistic early milestones and meet them. Without doing that, I have no reason to assume that you aren't another "idea guy" who thinks that Open Source conjures projects out of thin air. If you illustrate in practice that your vision is straight-forward, then it will be much easier to convince people that their contributions actually matter.
As harsh as this post sounded, I do not mean to be offensive. I just wanted to try to bring more constructive criticism into the thread. Best of luck to you!