you use monsters one level higher to make them more challenging... the result doesn´t differ too much from giving only +2 items instead of +3 items...
It does in a couple of parts of the equation. The formula for monsters isn't simply a 1 level=1 defenses, attack bonus, damage(per 2 levels), 8 hp. That's the quick method which works if you don't change a monster more than 3-4 levels in either direction. Even then, if you compare it to actual monsters of the level you changed it to, it'll be wrong. Not much wrong, however. If you increase it or decrease it more than 4 levels you start to notice nearly all the modifiers become 2 or 3 points off.
My point is that not differing "too much" is a big deal in a system as balanced as 4e. A difference in 1 of all the enemies defenses and attacks ends up causing about a 10% difference in the effectiveness of monsters. A difference of 4 can make the difference between a difficult encounter and an impossible one.
You usually keep the level around the PC levels, yes, but the DMG allows for scaling up monsters without giving major ability boosts, just hp, defense and attack and 1/2 damage per level.
As noted above, it advises not to go more than 5 levels. In my experience going more than 2 levels causes a minor problem and more than 4 causes a fairly big problem.
So tell me what is the didderence between adding +1 to all monsters defenses and attacks and some hp (like you do by using -2/+4 instead of -3/+3) or my approach (-1 attack/damage/defense due to lower level magic items)
I believe that +1 damage and the some hp cance each other out, so...
It depends if you continue the trend upwards. If the PCs have no magic item you give the level 30 monster -6 to attacks, defenses, -3 to damage, and -6x(hitpoints for its type). However, at the most extreme levels this causes an imbalance. I don't have monster stats in front of me right now. But I bet if you compare the resulting stats to a level 24 creature, it'll be off by a couple of points. A couple of points can be a big deal. I suspect it's damage will be very high in comparison to the level 24 creature but all it's defenses will be too low.
Of course, you also don't want to lower the damage of the monster, since nothing about the PCs hitpoints have changed due to a lack of magic items. So it's probably best not to lower the damage.
HP and damage probably do cancel each other out. But I can't say for certain. I know that giving people static modifiers equal to how much the magic items they are supposed to have give ends up with numbers that are identical to the ones in the math. Keep in mind that WOTC did a lot of work on the underlying math. Going as far as consulting with mathematicians in order to make sure the formula was correct. I know that it contains adjustments at certain levels. I'm not sure what they are all for.
To me, the biggest risk of this approach is in creating a pretty big imbalance in the PCs. If one character has a +5 weapon and another character has no magic items and you reduce all creatures by 6 levels...The character with the magic weapon will hit almost every time. So much that he can virtually guarantee his dailies hit with combat advantage and a buff from the leader. Meanwhile the other character will miss half the time and risks feeling kind of worthless.
I recommend either playing a magic itemless game with corrections for the math(either in the monsters or inherent bonuses to the PCs) or playing with magic items and making sure the PCs get appropriate magic items(1 magic item per PC per level).
I've also considered a hybrid system to keep magic items intact without giving out too many of them out. Basically you give the inherent bonuses to the PCs and then give out magic items that only have the properties and no enhancement bonuses. That way you could give out a "Lightning Weapon" and its ability continues to apply across all 30 levels and the PC would never have to get rid of it or replace it with another one. I think that would work pretty well. The benefits you get from magic items would be nice to have but small enough not to be necessary.
p.s.: i never told you level 9 against a level 1 party is appropriate... i just said this is the latest point to switch from normal to minion (same xp) you should use minions from about level 5-7 depending on your party composition...
I know you didn't. You said that you thought players should get the sense of getting better and they only got that if they still fought low level monsters. That defenses or hitpoints of creatures shouldn't get any better because then you don't feel like you get any better.
I was suggesting that it breaks down after a couple of levels if you don't scale the monsters. I suggest minions aren't necessarily the way to go either. Not only do minions not live up to the difficulty of a normal monster(even 4 of them aren't as good as one monster), but they still have scaled defenses and attacks. A 9th level minion is still going to feel harder to beat for a 9th level group than a 1st level non-minion.
And I strongly believe you are making a problem out of nothing... i never said magic items and monster levels don´t correlate (in fact i stated otherwise), but i believe using monsters of x levels lower where x is the difference between expected magic item bonus and available magic item bonus will give good results.
Mathematically giving a monster -1 to all defenses, attacks per plus of the magic items that the PCs should have will work out virtually identically to attack bonuses and defense bonuses. I'm not disagreeing with that. But there's a problem with hitpoints. You have no idea how many of the PCs will attack that enemy. If 4 PCs attack an enemy with +6 weapons and have a 50% chance to hit, then they do 12 points of damage extra per round. My best estimate in order to keep the monsters around for the same amount of time is to lower the monsters hitpoints by 4 times the enhancement bonus of the weapon they should have. This means that level 26 or higher monsters lose 24 hitpoints, level 1-5 monsters lose 4 hitpoints and so on.
Telling someone that magic items are a must have in 4e is IMHO wrong. There was somewhere a thread where a montecarlo simulation was used to simulate encounters... i bet, that increasing a monsters level and adding +1 to all big three items won´t change the result much...
Due to the above damage problem, I think it'll change the number of rounds monsters stay around. Likely they'll survive an extra round or two when you add levels to monsters and they'll die a round or two earlier when you remove levels.
Magic items are built into the math. WOTC has been pretty clear about this from the beginning. They specifically modified all of the stats of every monster in the game to account for it. You can fix the math with inherent bonuses equal to what is expected. But doing one or the other is kind of a requirement to avoid breaking the math.
