CUl is easy to get to around Rank 30, thats when it gets hard. I know some say R45 + but I think its more of a matter of opinion, how you like to level, what your expectations are.

Is this really a better method than simply doing leves?
Leves are great for SP, but once you hit around R46ish the sp starts dropping fast. I suggest taking advantage of quest SP. Hit up Zam and see which quests give the best completion SP bonus and do them on a DOW, turn it in as a CUL. That will help alot and with chocobos it will be alot less running than it used to be.

Also, has anyone tried abusing Hasty Hand to craft lots of mediocre SP recipes en mass for greater rewards?
It's not worth it IMO, especially once your in the higher ranks.

With the new changes to stats, is it worthwhile to stack piety and control, or do I need a decent amount of craftsmanship or mg. craftsmanship as well?
I can't speak to that as I have not touched CUL since a few days pre-patch. (Finally hit 50)

Is grinding sand still the fastest way to level CUL?
Grinding Sand is the best way to level into the low 30's, I think Northern Pike may be 37 so perhaps early 40's. The problem is they stacked 97% of the sand recipes in the first 30 ranks, with most of them being 1-20 for some god awful reason.

Is there anyway outside of trial and error to know if I should be using my primary or off-hand utensil for cooking?
I always use mainhand, never bothered experimenting since few over the population overall even looked at food.

Some other things I suggest is doing apple juice, herring balls and perhaps that sand recipe until sp turns to crap. Then move onto Aldgoat steaks, Orobon Stew (liver is easy now with new R15 dungeon).

Good Luck