...I only bought the 4e gift set, and I don't think I'll be buying any more 4e books unless something unbelievably cool & awesome comes out.

Hey, it's been known to happen

Anyway, back when I was running D&D 3.0 I ran into this really cool dark & gritty campaign setting called Scarred Lands. Since the official WotC campaign settings weren't doing it for me, I bought just about every book available to this campaign setting. Heck, when 3.5 came out and the campaign setting started dying, because about half the books were 3.0 and the rest were screwed up 3.5, I still kept on buying those books. Not because of the crunch: heavens no! The concepts, the ideas, the themes & moods were just so awesome!

Then I realized I was kicking a dead horse, which would only occasionally provide me with fun, if I was willing to go through a monstrous amount of work of actually fixing all the stupid mistakes that Sword & Sorcery Studios had put into the Scarred Lands books as far as crunch went. It didn't take me very long to realize that it was time to abandone D&D and move on to nWoD, which was just starting to come out

However, now I'm back to Scarred Lands: the setting that brought me back to D&D after a long vacation into various other RPGs during the 1990s.

I'm intrigued how easily I can pick and modify the monsters in the three Creature Collections I have? What about prestige classes in countless Scarred Lands books? Spells, magic items and artifacts from Relics & Rituals? Can I just pick up a magic item, glance at the 4e books, and go "Hm, this would probably work like that. Okay, implemented"?

How good is the streamlining across the board from 3.5?

I know, I'll get my gift set within the next couple of weeks, but I'm just curious.

It heavily depends upon the class, but rebalancing the powers to match currently existing powers should be easy. However, classes that are heavily focused around pieces that don't really exist in 4e(like grappling) or classes that focus on non-combat utility are going to be more difficult to do.
Magic items are fairly simple, but there are very few items with constant effects anymore, which was the mainstay of 3e magic items, and in general, the game has shifted away from magic item dependency, though magical weapons, armor, and neck-slot items are required to survive and prosper.

Ah Scarred Lands, home of great flavor and zero actual playtesting/editing. I have quite a few of the books myself and I'd have to say, converting them to 4e would be a challenge. Spells are mostly right out, but that's OK since most of the R&R spells were either useless or horrifically overpowered. Magic items vary widely, for example the Fang Dagger (IIRC) would probably convert pretty easily. PrC's might work as Paragon Paths in some cases, but would require a good bit of work. Where the setting was at it's best though was the monsters, and I believe converting your Creature Collections shouldn't be too difficult, so long as you concentrate on getting the flavor, not the mechanics.

This is excellent news. A lot of the books are filled to the brim with great fluff, but I would really hate to toss out all the great monsters that came with the Creature Collections and various others supplements.

Items will likely have to be toned down. Most items have 1 effect that occurs as a usable power, and perhaps a bonus with criticals (for weapons) or a secondary effect that is constant (smaller bonuses) but you can always go outside of that to create items that fit the flavor with fun daily abilities.