I'm very "impure" in my interfaces, but "pure" in the sense that I don't usually make any changes to the core "rules".
I use Therapist and love it. I really can't understand why some people don't like it, but if they don't, then they don't. Some people prefer EMACS instead of vim. There's no accounting for taste.
I also use some dfhack features:
* I'm using workflow more and more. It doesn't do anything I couldn't do manually, it just lets me skip all the tedious micromanagement. It's nice not having to queue up endless "smelt 30 limonite", "make 30 charcoal", "make 15 pig iron", "make 15 steel". Instead I just queue up repeat orders for each task and tell workflow to keep 10 iron, 10 charcoal, 10 pig iron and 30 steel on hand, and let it deal with suspending and unsuspending the orders as needed. I could do the exact same thing manually, but it would be tedious (and I don't think tedium is dwarfy). I just need to make sure to keep mining out ore and chopping down trees.
* Ditto for autobutcher. Not having to watch for a message telling me a Yak calf has grown into a bull so I know to butcher it is nice, but not exactly game changing.
* I use digv to avoid having to keep a constant eye on my miners the entire time they are digging out ore. I suppose that does give me some info I wouldn't have normally, but it's info I'd find in the process of micromanaging the digging anyway. Toady has said he's planning on adding similar functionality to the game anyway.
I tried autolabor, but found that after a couple of years, when I would normally have a legendary mason (as an example), I was instead having a bunch of low skill masons who took forever to make stuff. It seemed quicker to have one skilled mason who cranked stuff out quickly and occasionally have to wait for him to drink or sleep, rather than having masons always available to work, but so unskilled that they would take forever to get the work done. But maybe the autolabor algorithm has gotten better since then?
But I don't use reveal or any other dfhack features that provide info I wouldn't have access to via the DF interface, nor any that let me do things I wouldn't be able to do manually, like autodump, fastdwarf, or changevein. Oh, I have used drybuckets and cleanowned in the past to work around bugs, and would use similar functionality in the future as needed. If working around pain in the butt bugs is impure, then count me as impure.
I make various init and d_init tweaks like pop caps, FPS display, autosave, varied ground tiles, flow amounts, and pet burial. I wouldn't consider those to be "impure", since Toady clearly intended them to be changed as the player prefers. I also change the colors to a pallet that is a little more visible, so I can actually read text in dark blue on black. I also use a 16x16 ASCII font so my square rooms are actually square. But I came to dfhack from roguelikes (rogue, hack, larn, moria, angband, nethack), so ASCII works just fine for me.
I also usually modify announcement.txt to get rid of the damn pause and zoom every time a baby is born. I don't care when someone is born. But I'd pay Toady to add announcements when a dwarf starts starving or being dehydrated so I could pause and zoom to them to deal with it. I do care when someone is about to die. It's not like it would give me info I couldn't get by looking at the z->Health screen every few minutes. I also wouldn't mind an announcement for when a child becomes an adult so I can assign him/her some useful labors.
I'm not doing this in my current world, but I have played around with removing all the spamimal men so I could actually see an occasional animal. That would definitely qualify as changing the rules.
I can get by with the "pure" interface if I have to, but I see no reason to do so. I will play the first game year or so with it when a new release comes out, and by then DT and dfhack are usually updated. If they ever go away, I can live without them. But I see no reason to live without them now, just because they might go away at some point in the future. By that logic, I should not play DF, because Toady might quit working on
it at some point. Ditto for computers in general, electricity, soda and potato chips. Not using something that makes things easier or more enjoyable, just because you might not be able to use it in the future just seems silly to me.