Does the magnitude of math.random values affect performance?

The difference is almost completely negligible. I went ahead and ran a test, and the average difference between math.random(0,1) and math.random(0,100) is 9.5 microseconds (0.0000095 seconds.) You really don't need to worry.

In case you're wondering, this is script I used to figure that out:

local huget = {}
local smallt = {}
local hugeav = 0
local smallav = 0

for i = 1, 100 do
local t = tick()
print(math.random(0, 100))
table.insert(huget,tick()-t)
wait()
end

for i = 1, 100 do
local t = tick()
print(math.random(0,1))
table.insert(smallt,tick()-t)
wait()
end


for i,v in ipairs(huget) do
hugeav = hugeav + v
end
hugeav = hugeav/#huget

for i,v in ipairs(smallt) do
smallav = smallav + v
end
smallav = smallav/#smallt

print("average math.random(0,100) time: " .. hugeav)
print("average math.random(0,1) time: " .. smallav)