practiced solo stalls
Unless you're flying aerobatics or doing test flights, stalls are flight conditions that you need to avoid. You need to be able to recognise the signs of an impending stall and act upon them. And if worse comes to worst, you need to be able to recover from a stall but the recovery action from an actual stall is the same (in most aircraft) as from an impending stall.
During flight training, this is reinforced a few times by actually doing stalls and an instructor will not let you solo before you've shown that you can recognise a stall and execute a proper recovery. Likewise, during the flight test, and various subsequent checks after that, you'll be asked to demonstrate a stall recovery too.
But further than that, there's not a lot that you can practice about them. You cannot get "better" at stalls, perform them more accurately than the next pilot, or do them quicker or slower.
So I question the whole idea about "practicing" stalls, whether solo or dual, once you've shown that you can recognise a stall and recover from that.
There's a lot of stuff that you really can improve in, and some of these have been mentioned before. Rolling in and out of steep turns, slow/fast flight and transitions between them, landings, accurate heading/altitude keeping and so forth. Heck, even taxiing on the yellow line is a challenge sometimes. These are the ones that you can always strife for perfection for, and can really benefit from practicing.
(Edited: Not to say that you shouldn't be doing stalls whatsoever. Some people think stalls are fun, so if you want to do stalls for that reason, fine with me. In fact, in that case you should probably sign up for an Unusual Attitudes/Introduction to Aerobatics class. I'm just questioning the learning objective for doing stalls beyond the initial stall awareness/recovery stage.)