I value your opinion and have seen numerous references by you to the Topaz plugins.
Yes, they are really trying to innovate as far as post-processing is concerned (makes one wonder what happens if they were to add a Raw converter module). Topaz Clarity is a really good
addition to their suite of task oriented plugins. It can really revive an image from a bit dull to vivid, with much control left for the critical user, but also lots of opportunities to automate a workflow with presets, and really get good results fast.
I do have InFocus (which I understand is mainly useful for capture sharpening) for Photoshop, but have not used it that much because it is difficult to achieve optimal settings of the many parameters and it breaks the parametric editing of ACR by necessitating an intermediate TIFF.
The InFocus plugin is post-processing oriented, as all of their plugins, so basically everything that comes after a demosaicing operation of a Raw converter, including noise reduction, sharpening, masking, blending layers, color adjustments, etc., etc. They offer a really good price/performance ratio, since all updates (not just updates but also upgrades) to new versions have been free for previous owners of a licence.
Topaz InFocus (version 1) still needs a bit of work to appeal to a larger public, but it can be used in situations (e.g. smart objects) that e.g. FocusMagic doesn't handle, and sometimes it can produce better results. It is best at Capture sharpening type of operations, for Creative sharpening of lower spatial frequencies they have 'Detail'. It often helps to first upsample a file, then apply InFocus deconvolution, and maybe also some sharpening, and then downsample again. It seems to produce better deconvolution results on such undersampled data for some reason. That also makes it useful for Output sharpening after upsampling for output at the native printer resolution.
Lightroom is different to many other programs, in that it also does a lot of other useful things reasonably well, once you get to know the particularities like highlight compression and how to control that. The fact that LR does so in a parametric fashion is nice, because one always starts the processing from the start, but it also means that external processing usually needs to be based on rendered output, e.g. in the form of a TIFF.
Do the Lightroom Topaz plugins require a pixel rendered TIFF which has to be stored on disk?
Yes, unfortunately there is no way to avoid that, similar to Photoshop when you need to add adjustment layers (although Smart objects can sometimes allow to go back to the source). The upside is though that it often does things better than possible in LR. So if quality is paramount, I'm happy to pay the price of additional storage space. The quality improvements are really worthwhile.