Just to kill off some urban myths here before they perpetuate...
Disabling plugins will have virtually zero impact on startup time (it will at best be a difference measured in milliseconds, certainly not seconds). I have an 11K book library, twenty-something of my own plugins installed and enabled plus meme's Kindle Collections plugin, and all of the standard calibre plugins enabled. My library starts up in 5 seconds.
Secondly plugins will make zero difference to search time - they are not in the slightest bit involved in that process. The best thing you can do for search performance is twofold. Limiting the search terms advice I gave in my previous post above will make enormous difference if your habit is to just type your search words into the search bar without scope prefixes. Alternatively the advice from unboggling of using search prefixes is for optimum results.
I wouldn't think that rationalising your publishers will make any worthwhile difference to search times (particularly for the enormous ongoing and manual effort involved) though I agree for the OCD types it might be a warm fuzzy.
@microcity - if you have found that your library has sped up, I just don't believe plugins were the reason, it will have been something else that has changed. It could be a an OS update, an AV update, a calibre update, a custom column, a disk problem - but I can all but guarantee it will not have been a plugin as the cause.