Umm, maybe a stupid question here - but I want to clarify for myself:

Assuming; I do have the Gandalf hero and - lets say two lore heroes - as a line up, also enough resources on Gandalf. The topmost card of my deck is spirit and I also do have some spirit cards in my hand. I can play that topmost card (because Gandalfs ability). But can I also play any other spirit card from my hand (because now Gandalf has a spirit icon)? It is not said that he got his resource icon until end of phase or end of round. Thats why I hesitate....

Thanks in advance.

But there is written on Gandalf card :

(...) Once per phase, you may play the top card of your deck as if it was in your hand. When playing a card this way, Gandalf is considered to have the printed Leadership, Lore, Tactics, and Spirit icons.

So for me, it means that Gandalf has these sphere icons in order to play this one card only, not that he temporarily gains them for some time during any phase, so you cannot play any other card of any sphere from hand.

Yeah, he has the icons while you're playing the card and loses them again once you finish playing the card.

So you would say that Gandalf

- Can allow Strength of Arms to be played from the top of the deck

http://hallofbeorn.com/Cards/Details/Strength-of-Arms-TDF

- Will reduce the cost of Book of Eldacar if played from the top of the deck

http://hallofbeorn.com/Cards/Details/Book-of-Eldacar-EaAD

Because he counts as having them printed while playing them, but

- He does not count as a Spirit hero for Pelargir Shipwrite once Pelargir Shipwrite is in play, as the icon is lost once "playing the card" is done.

http://hallofbeorn.com/Cards/Details/Pelargir-Shipwright-AoO

So you would say that Gandalf

- Can allow Strength of Arms to be played from the top of the deck

http://hallofbeorn.com/Cards/Details/Strength-of-Arms-TDF

- Will reduce the cost of Book of Eldacar if played from the top of the deck

http://hallofbeorn.com/Cards/Details/Book-of-Eldacar-EaAD

Because he counts as having them printed while playing them, but

- He does not count as a Spirit hero for Pelargir Shipwrite once Pelargir Shipwrite is in play, as the icon is lost once "playing the card" is done.

http://hallofbeorn.com/Cards/Details/Pelargir-Shipwright-AoO

Correct.

Perhaps the most disappointing "Gandalf doesn't work here" situation is Lord Of Morthond, where he gains the necessary Leadership icon while the ally is being played but has lost it by the time "After you play an ally" would trigger.