I've installed a lot of stuff since 2005. Some of it is old and deprecated. Would you recommend redoing the plugins folder and making a new generation of cities?
i would. looks through the folder and looks at what's in there. Move what you can't do without or what was really hard to find into a safe place, and redo the plugins.
Many files have been updated since 2005 (like Simgoober his work as example) so I completely agree with dragonshardz in this to reorganize your plug-ins folder. Also the lots that are released now are often much more detailed (in textures) then the ones that were released before 2005 and many proppacks have been replaced since then so for your personal gaming experience I would recommend a day of reorganizing and re-installing.
Perhaps it's not needed to rebuild your cities (I don't know what you have installed) but to be safe I would buldoze every (ploppable) building and rebuild it after reorganisation just to be safe
Good luck!
A second generation of cities is planned. I have updated my lots often, but I feel like it's time for a fresh start.