Just an update on the situation with the next world.
Here are the parameters if someone wants to give it a shot, or just mess around with it. I did increase the embark points and lowered the layers between caverns and surface to just 10, but kept the layers above ground at 15 cause I've heard it causes lag. Can always add it in later with the infinitesky plugin from DFhack.
[WORLD_GEN]
[TITLE:SM DESERT REGION]
[SEED:uTv4xupDm6ZLNSWVgi7D]
[HISTORY_SEED:t9nMsJoO9bWQgi0ePtI9]
[NAME_SEED:6EZpPMWxM4E2u4y1lHGX]
[CREATURE_SEED:b5X2KsGsrTqmOe5clcHm]
[DIM:65:65]
[EMBARK_POINTS:2000]
[END_YEAR:200]
[BEAST_END_YEAR:100:50]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:0]
[ELEVATION:100:400:3000:3000]
[RAINFALL:0:100:125:125]
[TEMPERATURE:25:75:101:101]
[DRAINAGE:0:80:1000:1000]
[VOLCANISM:0:100:3200:3200]
[SAVAGERY:0:100:101:101]
[ELEVATION_FREQUENCY:1:1:1:1:1:1]
[RAIN_FREQUENCY:1:10:1:2:3:1]
[DRAINAGE_FREQUENCY:1:4:3:1:3:1]
[TEMPERATURE_FREQUENCY:1:1:1:1:1:1]
[SAVAGERY_FREQUENCY:4:1:1:1:1:10]
[VOLCANISM_FREQUENCY:1:1:1:1:1:10]
[POLE:NORTH_AND_SOUTH]
[MINERAL_SCARCITY:900]
[MEGABEAST_CAP:40]
[SEMIMEGABEAST_CAP:10]
[TITAN_NUMBER:60]
[TITAN_ATTACK_TRIGGER:80:0:100000]
[DEMON_NUMBER:33]
[NIGHT_TROLL_NUMBER:11]
[BOGEYMAN_NUMBER:11]
[VAMPIRE_NUMBER:11]
[WEREBEAST_NUMBER:11]
[SECRET_NUMBER:1000]
[REGIONAL_INTERACTION_NUMBER:22]
[DISTURBANCE_INTERACTION_NUMBER:22]
[EVIL_CLOUD_NUMBER:11]
[EVIL_RAIN_NUMBER:11]
[GENERATE_DIVINE_MATERIALS:0]
[GOOD_SQ_COUNTS:100:200:0]
[EVIL_SQ_COUNTS:100:200:0]
[PEAK_NUMBER_MIN:1]
[PARTIAL_OCEAN_EDGE_MIN:0]
[COMPLETE_OCEAN_EDGE_MIN:0]
[VOLCANO_MIN:10]
[REGION_COUNTS:SWAMP:180:0:0]
[REGION_COUNTS:DESERT:650:0:0]
[REGION_COUNTS:FOREST:180:0:0]
[REGION_COUNTS:MOUNTAINS:14:0:0]
[REGION_COUNTS:OCEAN:0:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:180:0:0]
[REGION_COUNTS:HILLS:10:0:0]
[EROSION_CYCLE_COUNT:100]
[RIVER_MINS:800:800]
[PERIODICALLY_ERODE_EXTREMES:1]
[OROGRAPHIC_PRECIPITATION:1]
[SUBREGION_MAX:3750]
[CAVERN_LAYER_COUNT:3]
[CAVERN_LAYER_OPENNESS_MIN:0]
[CAVERN_LAYER_OPENNESS_MAX:100]
[CAVERN_LAYER_PASSAGE_DENSITY_MIN:0]
[CAVERN_LAYER_PASSAGE_DENSITY_MAX:100]
[CAVERN_LAYER_WATER_MIN:0]
[CAVERN_LAYER_WATER_MAX:100]
[HAVE_BOTTOM_LAYER_1:1]
[HAVE_BOTTOM_LAYER_2:1]
[LEVELS_ABOVE_GROUND:15]
[LEVELS_ABOVE_LAYER_1:10]
[LEVELS_ABOVE_LAYER_2:1]
[LEVELS_ABOVE_LAYER_3:1]
[LEVELS_ABOVE_LAYER_4:1]
[LEVELS_ABOVE_LAYER_5:2]
[LEVELS_AT_BOTTOM:1]
[CAVE_MIN_SIZE:400]
[CAVE_MAX_SIZE:500]
[MOUNTAIN_CAVE_MIN:18]
[NON_MOUNTAIN_CAVE_MIN:30]
[ALL_CAVES_VISIBLE:0]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:25]
[TOTAL_CIV_POPULATION:15000]
[SITE_CAP:264]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:0:1356:240]
[RAIN_RANGES:1256:66:11]
[DRAINAGE_RANGES:1256:166:0]
[SAVAGERY_RANGES:66:0:1028]
[VOLCANISM_RANGES:33:264:568]
It does reject on average every 3000 worlds or so, but far less than it used to. I've genned about 6 worlds with fairly interesting sites at the moment. None are perfect though as is usually the case. I'll try to do up to ten worlds then narrow it down to 5 sites for voting. Have not spotted the volcano in the desert yet or the one that I am aiming at, which is a desert/ grassland/ haunted lake biome with access to iron, sand, clay, flux, no aquifers and towers. But I should have something up for voting by tomorrow.