My experience is that food/booze supplies are the strongest immigrant attractors. By far. My first few forts were always on the verge of starvation/thirst, and I got very few immigrants. In later forts I learned how to farm, how to fertilize (why does everybody hate potash-makers?), and that a stack or two of *roast* can usually buy everything I want from any caravan (just put it in rock pots to keep the treehuggers happy). Result: food stocks ~10x the head count and a second spring immigration wave of 35+ (ouch). Furnished bedrooms for all might nudge the average up slightly, but not much. My biggest 2nd-year migration set ever (37, 14, 22) came in a fort where everyone but a lucky 12 were sleeping in the dirt. Plenty of food, though. An siege/ambush my second winter, and sometimes another in the spring, is pretty much a given.
The amount of digging I've done for these forts has been pretty consistent, and I've never figured out how to get a good military going so my metal industry has been low-to-none. And yes, it's a bad idea to invite sieges your second year if you don't have a good military -- it takes months to build bridges and traps, even when my 4+ master miners clear out the space quickly. More than once the gobbos have arrived while I'm still putting up decorations for the party... fun.
I've never made crafts or decorated/encrusted anything, nor have I made clothing. It's not architectural wealth because I usually don't get started on big things like wells and dining halls until the big wave gives me cheap labor. I think my total fortress wealth typically hovers around 38k at that point.
FWIW I basically see no thieves/snatchers until after the big wave arrives, and often not until my second fall; they apparently assess value based on something other than food.
Also apparently the immigration jobs are weighted. For example if you don't have any farmers, expect to see a lot more migrant farmers, threshers and the like-- and some jobs are weighted more heavily than others. Farming is one, but I can't remember the others off the top of my head.
Fisherdwarves seem to be #1 (I usually accumulate a dozen of them by the time I hit 80 dwarves), followed by farming, followed by useless crafts. I never get miners (I train up 4+ myself), and seldom get masons/smiths/carpenters/mechancis even though I only ever have one of each of them. Oh, and I usually get a vampire my second summer or fall.