I'm working on an idea for a deck that's main idea if to get allies into and out of play to maximize the benefits they give when entering and/or leaving play. gandalf is the most obvious one, since his benefits are awesome, but others like Bofur (Spirit) and Descendant of Thorondor could also be good.

Prince Imrahil, Sneak Attack, Born Aloft, Horn of Gondor would all be good, but what else to include? What other heroes to use? What spheres?

Any suggestions are welcome!

Elrond would be a good hero because he can pay for any allies and can potentially play any card for free with Vilya which would be clutch with the afrementioned Gandalf or the eagles and such

The Rohan allies have nice synergies while not necessarily having to run all of them unlike the dwarves

Well you probably already know this, but Meneldor's Flight, Descendant of Thorondor, and Hama all make an amazing combo. It works better with a lot of enemies in play.

Ok, here is what I came up with so far. I think it would need some fine tuning, and som more reliable ways to make it more eaily repeatable.

Heroes:
Elrond
Leadership (Prince Imrohil?)
Tactics (Hama?)

Get Vilya onto Elrond. Use Vilya to put Gandalf into play. Put Born Aloft on Gandalf, and scoop him when he is done doing whatever he helped with. Gandalf goes back to your hand and Born Aloft into discard. Put Erebor hammersmith into play/play Second Breakfast to pull Born Aloft back to your hand. use Gildor Inglorion to put Gandalf back onto the top of the deck, rinse, repeat.

With this, assuming you do 3 Hammersmiths, Second Breakfast, Sneak Attack, and Gandalf, you should be able to put him into play a dozen times, if you went through the entire deck.

I am thinking there might be room for a copy or two of the Spirit card that shuffles your discard pile back into your deck, but if you cant get Vilya onto Elrond, the entire thing falls apart, and those Spirit cards are dead to you. :/

Suggestions for improvement?

I completely agree with including Hama. I've played him before and his ability is great for the type of deck you're trying to make. An added bonus is that he's not the type of guy you put in your deck just because of the ability. He has good attack, so find a way to make use of it.

Piece of advice: Don't try blocking with him. He's going to take at least one point of damage every time, and so won't survive long that way.

I haven't played either of the other heroes listed, so I can't really give an educated opinion on them. The deck itself looks pretty solird for the most part. Good luck!