The first way to scale back spells is to do away with non-slot cantrips or at-wills. The second is to put ritual and slot casting into the same system - a spell's a spell no matter how you cast it. The third is to make spells a bit more risky in some cases (see above); or maybe more costly, but that's annoying. The fourth is to look at how some spells got broken particularly by 3e (polymorph, anyone?) and fix them; and here 1e can give some decent guidance. A fifth would be to knock off some spells that trample on the niches of other classes (Knock, Find Traps, Spider Climb - or whatever their current equivalents are) and don't replace them. A sixth would be to make a bunch of spells currently with range of touch have range of self instead - Fly, Silence, Polymorph just to name a few - to rein them in. A seventh way would be to do away with metamagic feats. An eighth would be to do away with slot flexibility - if you're out of 1st level slots but you have some 2nd-level slots left then sorry, you're stuck with casting 2nd-level spells until tomorrow morning; your 1st-level spells are unavailable because you ran 'em out.
The thing I'd give them in return, were it me in charge of all this, is that spell pre-memorization would disappear never to return. All casters would work like 3e Sorcerers - if you have the spell in your book (or on your list, if a cleric) and you have a slot to cast it with then you can cast it. Period. Full wild-card by level. (I do it this way, and the pleasant side-effect has been that I see spells get cast that otherwise would never see the light of day)
Lan-"sometimes the most dangerous thing a 1e party has to face is the friendly fire from their own casters"-efan