For me, one of the bigger issues is world generation and ensuring an embark has all the features I want. More often than not, my tweaks fail or take an age, and it isn't easy to figure out how to ensure a successful tweak.
Another thing that I would like: A ballpark estimate of how much CPU & RAM an embark would require to run decently. I find that an embark over a certain size would cause DF to freeze.
Im not sure what you can do to regenerate a specific site, but with the powers of perfect world df and the built in world editor it should be possible to create a few template world types that fit in multiple useful objects adjacent to each other frequently. The issue would be in having both gauranteed embark sites and reasonable variation between worlds, because each template will generate the same parameters each time.
If its mostly resources a site lacks, then alternative reaction pathways for things might help, say if you ended up with no iron or flux, then some microcline and granite/gabbro (its almost impossible to find a site that has neither granite nor gabbro) can be combined to produce some iron or something useful, like silicate-bronze.
One of the best things i find is to have multiple civs you could trade with, which all have access to something like iron as a baseline and an outpost liaison for some of them you can make requests through. That will ensure you can trade more. Or fight more. Whatever, right?
So a useful mod for that is like increasing the carrying capacity of wagons and pack animals available to those civs. As long as you have something to trade, you can import what you lack. So maybe a couple extra trade product pathways would be worthwhile? I cant imagine being totally devoid of decent trade goods though
A Dfhack script might be able to estimate the z-level depth of a site and tell you, based on the number of tiles in that volume, how much RAM that site will use as a baseline. Cpu depends on flowing water, temperature, critters, pathable tiles etc so thats more situational, not easily predicted, right? But maybe a script can also predict that based on the average produced by the magma sea and 3 tiles worth of a river
Some simple science from players, available publicly, will also help establish averages for that, too.
Also, dorf civ variations shouldnt be too hard to come up with. In fact i think i had a faux-greek language i generated somewhere. At least i hope that wasnt on the thumb drive the puppy ate...