Double-clicking on the spawn rate buttons automatically set rate to max/min, which is very handy. The problem is that sometimes you are really just doing two (or more) single-clicks to get the spawn rate from "around the ballpark" to a particular specific number, but happen to do the clicks fast enough to trigger an unwanted double-click behavior instead.
namida mentioned in another thread that he recalls an IRS, possibly Cheapo, where right-click is used instead to trigger the "instant min/max" behavior. While perhaps less discoverable than double-clicking, it definitely does not suffer from the annoyance of unintentional double-clicks. It is at least worth consideration as an option (ie. right-click vs double-click, and possibly other sensible methods) the user can choose.