Hello @tompuri, I'm the author of the Ad Hoc Tags plugin (I actually call it "Ad Hoc HTML" these days).
I should point out that there are multiple plugins available to enable HTML tags (the others are all called "HtmlOK"). My plugin is very specific about giving the admin control over which HTML tags can be used and which are disabled, while the others just allow all HTML.
Of course, I can not say which of these approaches is the best for you. The way it is designed is specific for what I need for my own wikis.
This plugin also takes tight control over the attributes and enforces "best practices" in these. So if an attribute does not get rendered, it is either because it is not used according to the standards … or a bug in the plugin. Let me know about it if you think it is the latter :-)
In any case, you have already found the trick that you have to enable specific tags. I just wanted to point out that there are additional plugin that extend this one by allowing e.g. HTML tables, or MathML, if this is needed (the reasoning being that for most users this is not needed, and thus it makes no sense to include that into the main plugin.
Last but not least, I am usually popping in here in this Forum every now and then (though not really every day), so feel free to ask any additional questions. You can also contact me directly via the email address give on the plugin page, or via the GitHub pages.