"Open source" originally meant you published a tool, and you made the source available. Because of some projects that expected, and in some cases through licenses demanded that changes to the source code be resubmitted for sharing, "open source" now quite often adds the concept of collaborative development to the mix. I did (or attempt to do) the latter; allow me to share.
There are magnitudes of difference between the effort associated with source available and collaborative development open source.
Leadership: You need to tell people the who, what, where, when, why and how of changes. And very possibly, you'll need to diplomatically poke and prod your volunteers. You may need to define the vision and prioritize goals of the project, and then enforce them when someone tries to take things another way. And, unless you only want people to come across your tool through serendipity, you'll have to advertise, running that very thin line (even thinner on the Internet) between attention-getting and gaudy. If the project is going to implement the concept of meritocracy, as many open source proponents say should happen, then someone will have to judge people's accomplishments and dole out the rights and responsibilities appropriately.
Work flow: I haven't done an exhaustive search by any stretch of the imagination, but I have yet to see a collaborative development platform that did all the things I needed. Part of the point of open source collaborative development is that the quantity involved in code review will cover any potential issues in quality of code submissions; I haven't seen a free tool integrated into a collaborative development platform that helped manage that cleanly yet (e.g. counting code reviews; auto-promoting after x reviews). We had to handle that, hacking manual methods into the existing tools. Probably at some point you'll have to define a version and create a build. Then there's the grunt tasks like documentation. (Ever try to release a new version of something free without release notes? The furor!! grin)
PB-specific issues: PowerBuilder is a commercial tool, and while there are cheap versions available, there are not free versions. The DRM added to PB11 has probably reduced or eliminated piracy that developers were probably doing to take copies of their office PB home, and while PB11 and later have a dual license policy that would allow developers to take home a copy legally (with permission and cooperation of the original license owners to create a second license), I don't see a lot doing it. (No scientific study, that's just what I see.) That cuts down a lot of potential collaboration, even from enthusiasts. Issues of compatibility of code between versions of PowerBuilder, plus the fact that very few people will own every version, will limit again your list of potential contributors.
Don't get me wrong. I'd love to see more collaborative development open source in the PowerBuilder community. I'd love to know how to work out the issues myself, and I have an effort in the works to see if I can make a new model work. (My first effort to follow the popular model failed miserably, IMHO.)
Is there a reason to feel badly about firing a ZIP file up to the web and forgetting it? I don't know. Is there any more pride or embarrassment in a 4 year old ZIP file as opposed to a SourceForge project whose last contribution 3 1/2 years ago was a post "Where the heck is everyone?" There is a reason why Sybase CodeXchange devolved from a collaborative development platform to a source available platform: next to no one was using the collaborative development features. If you source available open source your code, you'll have plenty of company.
BTW, CodeXchange may be an answer to your concern about visibility to the PowerBuilder community, although you'll lose the web site traffic. The PowerBuilder Web Ring is another, significantly less effective, method to help your visibility that keeps traffic on your web site, but it demands a navigation bar on the target page on your site. CodeXchange may also be a way to get over your concerns about code quality and narrowness of purpose of what you have to share. grin
What should you do? Don't underestimate the effort with a collaborative development sharing, but don't let it stop you from a source available sharing.
Good luck,
Terry.