[Raynor]

Does Feanor pour some of his fiery spirit into the Silmarils as Sauron pours some of his into the Ring?

I think that the following passage from Of the flight of the noldor, Silmarillion is relevant:

Yavanna spoke before the Valar, saying:
- The Light of the Trees has passed away, and lives now only in the Silmarils of Feanor. Foresighted was he! Even for those who are mightiest under Iluvatar there is some work that they may accomplish once, and once only. The Light of the Trees I brought into being, and within Ea I can do so never again. Yet had I but a little of that light I could recall life to the Trees, ere their roots decay; and then our hurt should be healed, and the
malice of Melkor be confounded.'
...
Feanor spoke then, and cried bitterly:
- For the less even as for the greater there is some deed that he may accomplish but once only; and in that deed his heart shall rest. It may be that I can unlock my jewels, but never again shall I make their like

There is either a limit on the sub-creative power or a limit on creating unique objects: Yavanna can only make the Trees once, Feanor can make the silmarils once.

I don't thinkt that the wizards imbued their staffs with a tremendous amount of energy of their own, but it could be that at least for Saruman this is an irrepeatable act.