That all makes sense. However, was my patch complex ;-)?
I think the one thing about ISPConfig compared to modern web systems is the UI. I have exactly the same problem on my project, fighting that now possibly more than 50% of development effort is expected to be on UI design rather than functionality, and that newer systems make more use of what can be done in a post-IE7 world due to a lack of legacy decisions. And in fact, I think cPanel, and other big control panels with old roots, have the same problem. That kind of thing, and themes, don't require such intimate systems knowledge.
I'd say it's an opportunity to you. You don't need to merge in the forks if you don't wish to (on a case-by-case basis). With my project I actually have people sponsor development, and to my surprise someone recently was willing to pay me to merge someone else's patches in. So I think it could work for you. You need to get the communication right of course.
Lead developer, ocPortal CMS (http://ocportal.com/
). Much better than Drupal/Joomla/Wordpress ;-).