Here you lose me. Simple kobolds? What do you mean? What would it change if they were duergar?
SkidAce understands me rightly; expectations about the monsters available resources.
Coming as I do from 1e, the sort of resources available to a monster were well defined - how many would appear, how many would have armor, what sort of weapons each would carry and in what proportions, how many seige engines was available to a tribe, how many pets and of what sort the tribe might have, how many leveled individuals would exist within it, what chance a spell caster was available, and the total worth of valuable goods owned by the tribe was. The DM of course could invoke Rule Zero to alter the situation as he saw fit, but if he altered the resources available to a tribe very significantly, he could no more claim to be using kobolds than if all the kobolds had 4HD. One of the implicit assumptions of defeating a party with 'merely kobolds' is that the foe is 'merely kobolds' as defined in the MM. If in fact the kobolds are 4HD, wear platemail, and have magic weapons they aren't 'merely kobolds'. Quite obviously, if you provide a foe with enough resources, the foe becomes challenging, but equally obviously you aren't emphasizing the fact that your 'mere kobolds' are defeating the PC's through cunning and intelligence, but rather by virtue of having 4HD and a +6 bonus to hit. By making them 'kobolds' are you trying to pretend you are doing something impressive - that DM that can 'beat' the PC's with mere kobolds?
It's never impressive when a DM beats the PC's. The DM can ALWAYS beat the PC's. There are some DM's that struggle with this, but they are usually the ones that can't throw their subconscious sense of fairness out the window.
What I'm suggesting here is that if you feel the need to attack the party with a group of monsters with every possible material advantage, don't make the mistake of fooling yourself as the DM by making those monsters 'kobolds', because in doing so you are probably giving in to a desire to flatter yourself. Instead, if you really must make the monsters high tech foes with extensive magic, high level leaders, omniscient understanding, telepathic levels of coordination, and seemingly unlimited resources, consider how you feel different about your creations if you make the Duergar or Drow or some other race already known for having all of these things.
Everyone knows that treating Drow in this fashion is 'cheese', and Drow are the original 'Gary's Kobolds' - humanoid foes which can face the PC's having every possible advantage. Relabelling such a foe as 'kobolds' when they are clearly not strikes me as something DMs do when their underlying motivation is to win acclaim from their players for the DMs cunning and nastiness, but I think they are likely to be disappointed in that regard. Whether kobolds or drow, if I get the feeling that a particular race is acting as the DM's PC - the thing in the setting he identifies with and has vested his ego in and which he will therefore not allow them to be less than impressive - then I'm probably not going to be impressed. I'll be much more impressed by a DM's restraint in this matter - foes with limited resources, weaknesses, imperfect defenses, and so forth. The less you go beyond them being 'merely kobolds', and the more challenge you can manage while being fair and reasonable, the more impressed with your design I'll be.
This is why, if your intention is to 'help me make them shiver at the sight of a kobold', I'm very skeptical that you've retained or will be able to retain your proper distance and neutrality in your role as DM as referee. I'm skeptical entirely of the goal you are setting out, and so suggest, does, "help me make them shiver at the sight of a duergar" have the same ring to it? If you must use kobolds as an excercise in design, first use actual kobolds, and secondly understand that its a pretty trivial excercise in design for an experienced DM. The only trick is realizing the kobolds are irrelevant to the scenario and have no real role in providing the challenge. They are there mainly to personalize the real threat, in the way that Acererak personalizes the threat of the Tomb of Horrors even though he's not visible through most of it.
I can help you with your goals. I can make PC's shiver at the sight of kobolds. But what is the point really here? It's pointless for the DM to prove he can challenge the players. It's a trivially easy excercise to create wholly unfair situations. What do you really want?
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