I'm a perennial student, I guess. Still trying to be able to improvise jazz lines in thirds (split between the two hands), so I do some weird scales every day, like a diminished scale in thirds for three or four octaves, then down in major.
I got that idea of "switching" at the top of the scale from minor or diminished from the first bit of the last movement of Beethoven's Op. 27 no. 1.
I don't know how long until I get bored of it, but I do like the sound of lines played in thirds, and lord knows my Chopin Op. 28 #3 (G) needs help, so I've got to work on my left hand.
ETA the other scale-oriented work focusing on LH I use as both music and as an excuse to do LH scales is the contrapunctus 9 from Ars fuga. It's challenging to memorize all of it, so I'm devising some strategies to just deal with the first 60 bars. Fortunately it's pretty amusing, so I'm not sick of it yet.
EETA I probably should add one of my little practice tricks I started doing a few weeks ago. It's also a scale-practicing trick, but it keeps me amused. So for a long time I've been doing various rhythm-changes heads (Anthropology, Oleo, Eternal Triangle, etc) in LH, so I just play a tune like "Parisian Thoroughfare" and switch mid-phrase from playing the melody iin RH to LH, and back and forth. It's pretty tricky, and no one would mistake it for music, but it has the advantage of keeping my brain active, to some extent.