I see no reason why you would want to practice spins, unless doing an FI course, or practicing for aerobatics.
As for PFLs, I have practiced this many times on my own, or with passengers on board. The main problem with a student doing it would be forgetting to warm the engine, or advancing the throttle too violently on the go around causing a real engine failure.
There is also the 500' rule to be aware of, which is fine if you've got an instructor next to you keeping an eye on it but not so good when you're on your own and also trying to fly the plane.
If you're not comfortable practicing something on your own, it's probably an indication that you need to practice it more with an instructor.