Webwork - 1:05 pm on May 7, 2012 (gmt 0) [edited by: Webwork at 1:45 pm (utc) on May 7, 2012]
the more i think about it, the more i'm put off doing wordpress plugins
Which is probably sound justification for NOT attaching a penalty to "plugin credit links" - i.e., the plugin author lacks utilization control AND Google may not wish to crap up the developer ecosystem of the Web's most popular content management system by effectively penalizing plugin creators.
It' comes as no surprise to me that a search for "Wordpress SEO" brings up, as a top result, the website of a developer of some popular WP plugins - even though many others speak to the issue of WP SEO.
I can imagine scenarios other than WP specific ranking issues where helpful industry specific plugins might lend an advantage - in topically relevant queries beyond just plugin queries - for the plugin developer.
Of course, in most cases, it likely takes effort beyond simply producing a plugin to gain all the possible advantages of plugin creation. However, plugin creation - as part of a larger marketing/profile building (as an industry expert, etc) strategy certainly has the potential to lend weight to your expertise/"authority in the industry", your standing "as an author", your "inbound value votes", etc.
Plugin development, woven into a larger strategy of topical authority building, probably works FAR better than plugin building simply for the sake of link aggregation. The multiplier effects of plugin development likely come from the fact that many "talk about how to do X" whilst the plugin developer directly helps you to "do X", does it for you, etc. Lots of love for that type of work in a world looking for more with less or struggling with limited ability, limited resources, etc.
[edited by: Webwork at 1:45 pm (utc) on May 7, 2012]