Just saw a post here from Wulfrock on a custom mod to fix sandstone vein counts:
What I would like to see is a mod like this, but that expands on the idea to include all vein types, allowing you to set an ore range for each type. So if you want Glimmer and Addy veins to be higher than 50, but not as high as iron, presto. I agree with Wulfrock that sandstone is too plentiful for full 10k veins, so setting a lower count is going to be preferable for most server hosts. If there was a mod like this before I'd created my server, I would have created more veins, but with smaller quantities in each, to provide greater access to all the different ore types, without making it too impossible to mine in a straight line.