Somehow I missed this, maybe that was best.
I think you've answer most of your questions, is it worth working on it? Only if you want to get good and frustrated followed by a nice cold adult beverage. Or two.
I would start by trying to get the neck off, that will answer a lot of questions - type of joint, whether you can change its angle. As you know I believe everything starts with the geometry, if you can't get it workable you are doomed from the start. I have a little steamer that I would try, its either going to come apart or not. It probably is a dovetail, the glue is weird looking and I'm guessing that is the end of the truss rod sticking our of the neck block.
If it won't steam apart you can saw the neck off as per the other thread, put a couple of inserts in the heel and bolt the sucker back on. The heel crack worries me, it obviously is a stacked heel which should be nice and strong but the inserts run the risk of splitting it more.
I know you are starting to dabble in slide and I play a bit too, my feeling is that you don't need or necessarily want big high action unless you are going to play strictly lap style, in that case throw a nut extender on it, maybe make a new tall flat saddle insert and slide on in. A lot of very good players do play lap style on acoustic guitars - Kelly Joe Phelps, John Fahey, Jerry Douglas (mostly dobro).
The way I play slide involves mixing fretted notes with the slide notes and you just can't do that with sky high action. You may find that what you've got will work OK. The other problem with my slide guitars is they are in open D or G or something and I play a bunch of nice non-slide songs in those tunings.
You've got a couple of other options. You can pull the fretboard (heat and pallet knives assuming the glue will release. That lets you futz around with the truss rod - replace or whatever it needs. You can also level the top of the neck and improve the relief situation, refret as required.
The bridge looks like ones that appeared on some Epiphones and Yamahas during he 70's. They were adjustable, some people didn't like them, parts get lost and are hard to purchase. I've converted a couple to standard slot without the channel, I would say if you are successful with the neck it might be worth while doing it to this one.
You asked about compression fretting to get rid of some of the relief. I've never done it, its one of those mumble jumble things that some of the legendary repair techs do with old Martins. Fretwire with thicker tangs is available, Erlewine talks about it in his book on repairs. Post pictures if you try.,
So bottom line, its going to be a totally frustrating experience whatever you do with it. I'll be there is a family of house finches that would love to move in and chirp and sing and enjoy their new housee.