It is possible to generate a dense ores world with only minimal instability. By that I mean it is possible to generate a dense ores world where you only suffer a few minor sickenesses that can easily be blocked by a roof.
I've created a few of these and although there is no guarantee, here's what I'd recommend:
1. Use only 1 dense ores symbol.
2. Stick as close to normal as possible (normal biome generation, normal day/night, normal weather, etc).
3. Make sure you have 10 or more symbols. I have found that adding biomes along with normal biome generation (which overrides the biomes anyway) is a great way to pad the age so that 1st entry doesn't add some horrible extras (like meteors!).
Then... test. Using this approach I usually go through 4-5 duds (decay, meteors... even a random extra "void" symbol once) before I end up with a world that has minor sickness. Then I can just dig underground, which I was intending to do anyway, and get to mining in peace.
There's nothing like hitting a 10+ block diamond node every 20-30 blocks.