I'd have to disagree with you to a point, Pax. Very few people can afford to build and maintain skill using what we would consider "carry" ammo. I like to shoot at least 100 rounds a week with whatever gun I'm carrying, which would work out to about $50 with my carry ammo. It's just [not] possible for me to spend $200 a month on ammo.
Marksmanship is about not only hitting the target, but about doing so consistently. If I fire 100 rounds of $4.00 a box Blazers at a target and put 90% of them into a three-inch area, that's pretty consistent. If the point of impact is two or three inches low, so what? I'm doing all the right things, including trigger control and breathing, and sight picture must be pretty consistent as well.
After learning to maintain that three-inch group. it's now time to put it on target, which is why my guns are all sighted in with my carry ammuntion, not with the everyday stuff. It's imperative to practice sometimes with the expensive carrying ammunition, but I don't see any reason why practice sessions should revolve around nothing but the default ammo. Any practice is good practice if it teaches me something or further hones a skill.
All that having been said, I have a short list of ammunition I'll shoot in practice. It's a list I've developed through mostly trial and error, and while it's not carved in stone, it's very firm in my mind.