I just installed trial version of Topaz Detail,it looks to be quite decent,but is buying it justified? So many ways to sharpen images with PS,is this plugin able to do things that PS on it's own cant?

See what you can do with Topaz Detail vs with Photoshop alone on the image in this thread:

https://www.modelmayhem.com/po.php?thread_id=931073

I'm curious to hear what you think.

Also I'm finding that Topaz controls local micro-contrast. It's not just a sharpener.

Fixel Detailizer (in the same thread) seems to be more just a sharpener.

I use it and a couple other Topaz products. Never globally but on layers to control the effect. I like it.

worth it to me, or to you?

You are in a much better position to decide that than I am.
If the primary use is to sharpen, then I would say no, but
if it fits well in your workflow, then?

Try Calvin Hollywood "freaky details" technique, you can make an action.