Supernatural signs and segulos

The Gemara in Horayos lists off 2 kinds of supernatural signs/segulos.

1. What we would call today segolus
2. Supernatural signs/omens of what the future will hold

Segulos

The Gemara has the following:

1. We anoint kings only by a spring, for an omen that their kingship should last
2.  One should eat on Rosh Hashanah gourds, fenugreek (Rashi - clover) leeks, beets and dates so that we should have a good year

Signs/Omens

The Gemara has the following:

1. R. Ami: If one wants to know if he will survive the coming year, he should hang a lamp during the 10 days between Rosh Hashanah and Yom Kipur in a house in which wind does not blow. If all the oil burns, this shows that he will live.
2. If one wants to start a business venture, and wants to know if it will succeed, he should raise a chicken. If it grows fat, he will succeed.

The obvious question on all of this is how does this fit with תמים תהיה אחרי ה' אלוקיך and the issur of ניחוש?

The rishonim give various answers none of them very convincing.