[MENTION=386]LostSoul[/MENTION] is the only 4e GM around here who I know runs a sandbox (maybe [MENTION=1210]the Jester[/MENTION] too?). Maybe they can tell us how they use minions (if at all).
Yep, I run a sandbox.
Yes, I use minions. I use them a lot, and sometimes I use a lot of them.
If the basic question here- and I haven't been following this thread for the last, like, week or something- is how a sandbox works in 4e vis-a-vis monsters when the pcs hit it at different levels, let me give you an example.
Early in my current 4e group's career, they found a big ass dungeon beneath a fissure opened up by an earthquake. They found it at first or second level, made a few forays in and managed to gain the allegiance of some goblins in there. Deeper levels included tougher monsters: a pair of wererats with a baby purple dragon, durgar, eventually a level of troglodytes suffering from internecine religious war... and so on.
The pcs are now in the mid-20s, levelwise, and have returned to the same dungeon. The demographics of the dungeon have changed in the meantime, with a troglodyte cleric and his allies having killed most of their own people and animated them as zombies.
So what stats am I using as the pcs explore? Basically, I'm doing three things.
1. Encounters with one, or even a few, of the trog zombies get handwaved. "As you guys move into the next chamber, you see a pair of the shambling zombies start to stagger toward you. You easily dispatch them." Generally there's not even any need for dice.
2. Encounters with many of the trogzombs are played out, treating each mass of trogzombs as a swarm (custom stats on this).
3. Then, of course, there are a few heavy hitting monsters down there that can work as-is: a dragon turtle (alas, they already killed it), some high-level evil leader types, etc.
That doesn't address the minion question directly, but it shows what I do when we step
beyond the point at which a given monster would be 'minionized.'
Now, let's take the example of giants. Near the end of their paragon tier adventures, the pcs made enemies of a tribe of frost giants. At the time I was using standard mid-teen-levels frost giants for most of their stats. When a band of them attacked the party some levels later, I rewrote their leader's stat block from an elite level 19 or thereabouts to a standard monster a few levels higher (I usually try to make the xp values roughly equal when I do this) and rewrote the rest of them into level 21 or 22 minions.
In 4e, the stats a monster wears at a given moment aren't absolute. They're relative to the party. I think that's one of the issues a lot of folks have with it, but because of the rate the math changes at, you kind of have to accept this if you want to make the system sing.
As far as higher level minions- I don't have a problem with e.g. the 1st level pcs encountering 4th level minions. I wouldn't build that encounter as a matter of course, though. The thing about that kind of encounter is that you have to ask yourself, as the dm, how you want the pcs to perceive the monster in question. Sticking to duergar as an example, if you want the pcs to perceive duergar as a bunch of bad asses that they need to be wary of, wait on the minions until the pcs have had a chance to deal with several of the "standard" duergar. But if the pcs raid a duergar fort and find the less-combative types (e.g. the old retired guy with one leg, the women and children, if duergar have the stereotypical dwarven patriarchal society, etc), minions are perfect for representing them.
I use minions in two basic ways: 1. Cannon fodder and 2. To represent creatures that aren't a significant individual threat due to pc competence.
I'm not sure if that answers the question adequately, but I would be happy to go into more specifics if anyone has further questions for me.