Scaling upward has been a hot topic. Here's some thoughts:
Depending on the version of D&D your talking about, scaling was much different. I usually have Moldvay, 3E and 4E books on hand for reference, and there's some pretty dramatic differences. Moldvay's scaling is mostly minimal. 3E is all over the place, without GM permissions (in the form of magic items) or help from a caster, fighters never really scale, but casters scale dramatically. 4E has such tightly coupled scaling that it's nearly transparent: your damage increases at the same rate as monster HP.
Those also all have the modifier of to-hit rolls. In DW, monsters are (unless a special move applies) all about as hard to hit.
Our current plan for DW (only part of which is in the PDF) is to have player damage and monster HP scale slowly. Dealing extra damage should reflect a player's choice of moves, not a dull required move or some automatic advancement.
The bigger part of scaling is monster damage and player HP, which has a more dramatic progression. A higher level monster does more damage (and may be causing more Saving Throws).
I guess the short answer is: scaling is definitely a part of play, but in a more considered way. The main part of scaling is that higher level monsters are more dangerous, so you'd better have a plan to survive long enough to take them down. And of course they're not just more dangerous in the sense that they deal more damage, they have fictional abilities that make, say, staring a dragon in the eyes a bad decision.
As for using old-school adventures, I'll have to guess a little more on this one. I've never ran a classic old-school D&D adventure, so I have to speculate a little.
Since DW (like AW) is fiction-first, I think it should be pretty doable. I think the important mental step is to take the descriptions in the adventure, particularly the stats, and think about what they mean, fictionally. Room 24 of the Caves of Chaos in Keep on the Borderlands, for example, has stats for a whip that will "jerk the victim off his or her feet and stun (paralyze) him or her for 1-2 melee rounds." Those stats don't come across directly, so on the fly I'd probably come up with a GM move related to the whip-wielding hobgoblin to represent that: "Hold someone stunned for a moment" or maybe "Take away their ability to fight, momentarily."
That's maybe the toughest part. I never played enough Moldvay to make sense of the abbreviated stat block on the fly, so information could be hiding there that I wouldn't know to represent fictionally. But generally, I think you can just translate the original mechanical and fictional descriptions into pure fiction, then apply them to DW.
The great thing is, that fiction can come across to DW without a lot of rules work. In the example above, I didn't mess with damage or make a full-on custom move or anything. I just stated that, fictionally, this hobgoblin can knock you out of the fight for a moment with a whip crack. Of course there's many ways to represent that, if this hobgoblin was a big deal, or I had a great idea for a custom move, I might make it into a custom player move: "When you're struck by the hobgoblin slaver's whip..."
The other part of bringing an adventure across is fronts, and I think we're pretty well covered here. Our front types are actually based on Adam's awesome job of looking through mounds of old modules and describing the threats in each. Taking, say, Keep on the Borderlands, you can easily start making adventure fronts, and even come up with a campaign front to tie it all together if you like.
The process of making fronts is likely to change the nature of the adventure a little. You could, I guess, play without fronts, and just run the adventure as-is, but I think making fronts would actually be a great way to bring the adventure to life.