Re. error checking, I think that it’s worth taking into account the “target audience”.
With some types of plug-ins (such as this one, my “wave stats” and “sample printer”), these are “technical” plug-ins that are only of interest to “geeks”, who should realise that if you enter stupid values, you will get stupid results.
In comparison, plug-ins such as the “notch filter” that Bill and I spent so much time on, are aimed at being useful to “general users”, and as such should be idiot proof/bullet proof.
For “technical” plug-ins I think that it is sufficient if it is clear how to use the plug-in correctly.