As long as similar modules contain unique features, I don't think there's much of a problem,
Wrong, this is exactly the problem. I just spend two days evaluating the 5 or 6 different 'aggregator enhanced' modules out there, and finally picked one, founding none of them completely satisfying, while most of them having really great bits. Quite frustrating.
Maybe you aught to submit an issue with your suggestions to the "closest" module? Many enhancements I made were based on such submissions. I'd hate to say this, but some contributed modules are so badly written, so badly documented, that patching them up would be a living nightmare (trust me, I WAS there). Sometimes the best way to produce something excellent is to simply not base it on something severely flawed (I'm not mentioning any modules here! Some aggregation modules were launched parallel or even after mine I hadn't even tried them, so I'm not even implying any module here! Some modules are simply so spectacular it's silly to go about inventing the wheel again.) Some had the logic thrown right into them in a pretty ugly way. I attempted to create a module that's extremely clean, extensible and efficient. So it's a software engineering standpoint that made it the right decision.
but the time and efforts of developpers and of the community at large (debugging, reviewing, patch submitting...) are generally best put into enriching / >strengthening an existing module when possible instead of being spilled over 5 or >six different contribs.
Better that than wasting developer and community time searching for bugs in spaghetti code :-) I'm sure no one would say that creating drupal should have gone into enhancing another CMS ;-)