You don't need high rainfall to have murky pools useable year round. Just turn the murky pool into a rainwater collector with the actual pool down below it. Water will trickle into your reservoir every time it rains, it will never dry up as long as you keep it at least 2 deep, and you can use it just like the murky pools - fishing, irrigation, drinking water, etc.
As far as world generation, the mesh size and weighted ranges are very powerful for affecting how the world generates. I like setting my weights to 1 1 3 2 1 on the elevation, this gives you more tiles in the upper end which generates more mountainous areas, which means a larger goblin and dwarven civ area as well as more good embark areas near mountains. Elevation apparently reduces aquifers too.
Heres an example of world gen parameters that will make a big mountainous island with ocean all around it.
[TITLE:INFINITE WORLD]
[SEED:7777777]
[HISTORY_SEED:2010]
[NAME_SEED:2010]
[CREATURE_SEED:2010]
[DIM:129:129]
[EMBARK_POINTS:1500]
[END_YEAR:1050]
[BEAST_END_YEAR:200:80]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:0]
[ELEVATION:1:400:1600:1600]
[RAINFALL:0:100:200:200]
[TEMPERATURE:25:75:200:200]
[DRAINAGE:0:100:200:200]
[VOLCANISM:0:100:200:200]
[SAVAGERY:0:100:200:200]
[ELEVATION_FREQUENCY:4:1:1:3:2:1]
[RAIN_FREQUENCY:1:1:1:1:1:1]
[DRAINAGE_FREQUENCY:1:1:1:1:1:1]
[TEMPERATURE_FREQUENCY:1:1:1:1:1:1]
[SAVAGERY_FREQUENCY:1:1:1:1:1:1]
[VOLCANISM_FREQUENCY:1:1:1:1:1:1]
[TITAN_NUMBER:9]
[TITAN_ATTACK_TRIGGER:80:0:100000]
[DEMON_NUMBER:28]
[GOOD_SQ_COUNTS:6:63:0]
[EVIL_SQ_COUNTS:6:63:0]
[PEAK_NUMBER_MIN:5]
[PARTIAL_OCEAN_EDGE_MIN:0]
[COMPLETE_OCEAN_EDGE_MIN:4]
[VOLCANO_MIN:3]
[REGION_COUNTS:SWAMP:66:0:0]
[REGION_COUNTS:DESERT:66:0:0]
[REGION_COUNTS:FOREST:264:3:0]
[REGION_COUNTS:MOUNTAINS:2112:6:0]
[REGION_COUNTS:OCEAN:0:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:528:2:0]
[REGION_COUNTS:HILLS:528:2:0]
[EROSION_CYCLE_COUNT:250]
[RIVER_MINS:25:25]
[PERIODICALLY_ERODE_EXTREMES:1]
[OROGRAPHIC_PRECIPITATION:1]
[SUBREGION_MAX:2750]
[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:1]
[LEVELS_ABOVE_LAYER_1:6]
[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:5]
[CAVE_MIN_SIZE:5]
[CAVE_MAX_SIZE:25]
[MOUNTAIN_CAVE_MIN:5]
[NON_MOUNTAIN_CAVE_MIN:10]
[ALL_CAVES_VISIBLE:1]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:12]
[TOTAL_CIV_POPULATION:20000]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:1056:1056:528]
[RAIN_RANGES:528:1056:528]
[DRAINAGE_RANGES:528:1056:528]
[SAVAGERY_RANGES:528:1056:528]
[VOLCANISM_RANGES:528:1056:528]
What makes this world the way it is is primarily the elevation settings. You could do the same with high volcanism to make tons of volcanos (set the weight of 80-100 volcanism to a higher number). The mesh size/weightings are really the most powerful setting in world gen. They affect how the world generates, while most of the other stuff just triggers rejections if it isn't present.
Oh, and that example generation is actually a really good world, but it has so much going on in it (due to increased civilizations and the ability for the goblins to spread far and wide and war with everyone) that it takes forever to generate to 1050, genning it to a lower year would be faster. It has tons of places with sand and flux and rivers and such. I posted about a great site in it
here if anyone is curious.