Should we be worried about the various curses of the chachamim of the gemara? Does this effect practil halacha in any way? For example, one who bows toward a rainbow, one who prays mincha close to sunset or one who renegs on a deal. All recieve a curse.
Yes though it might depend.
For example buying and selling items there is a curse of "mi she'parah" that if one side (usually the seller) backs out of the sale after it has been confirmed (ie: money transferred), they are subject to a curse. Perhaps it needs a Court to make it take effect, or perhaps Hashem will enforce it anyway. I suppose that might depend on your outlook.