Council of Elrond

Background
I broke out my ME:CCG collection that hasn't seen play in 20+ years. I've been toying around with the Challenge Decks the past few days and reading up on Arda. Just to see how many cards I had, I started copying Gandalf Gene's Arda deck, and I probably have ~50% of the needed cards. While browsing around, I noticed there are a handful of cards selling on eBay for $100, notably some of the AtS R1s. I found I have a single copy of Agburanar / Itangast / Scorba Roused, and The Ithil-Stone. I'd like help figuring out what to do with them.

Questions
Why are these cards worth so much? And do they go into very specific deck lists, or are they generally good in any deck?
As a casual player, are these worth holding onto, or should I sell them to purchase a bunch of other cards -- potentially filling out enough to complete an Arda list?

Bonus Question
I have a sealed booster box of Wizards Unlimited. Is it worth it to crack this open to fill out an Arda build? Or would it be a better idea to sell the box and buy singles?

Years ago, I sold some rare Magic cards (couple of P9 and spare duals) to fund purchasing enough cards for a powered Cube, and it's now my most treasured gaming item. I'm leaning towards doing the same thing here -- selling these 4 cards and using the results to build an Arda. For a casual player, is that a good idea, like it was for Magic?

Thanks for the help!

If you're not going to use them, sell them. They're valuable because they're rare, but I don't think any of them are particularly useful in constructed play. Also, Agburanar Roused and Scorba Roused are both from The Lidless Eye and are worth far less than Bairanax, Daelomin, Earcaraxe, Itangast, and Leucaruth Roused.

That said, if you plan on making a Minion Arda deck, the world can certainly use another one of those (as far as I know, Goblin King's and mine are the only two, and I think his is partially proxied), and the decklist for that includes a copy of each of the <dragon> Roused factions. At the end of the day, it's up to you, but I've been quite happy to get rid of my own spare cards, no matter how valuable on the market, to get cards I'm actually going to use and play with.

Of the cards you listed, only Itangast Roused and The Ithil-stone are R1. They are not very good cards to play with, and are valuable solely because of their extreme rarity for collectors. AtS as a whole was a low print run, and R1 was the rarest designation that I.C.E. printed outside of maybe some promos.

If you want to sell them, I'm sure you'll find a buyer. That said, you might get more trading them here, as many of the cards you'll want for an Arda deck are commonly available for trade.

Anyhow, that's my two cents.

Thank you for the feedback, exactly what I was looking for. If they're not very playable, I'll be much happier selling (or trading) for playable cards. I didn't realize there were "Roused" cards from The Lidless Eye, I didn't do my homework! Cheers to both of you.