strip_unit.rb

require 'sass'
module Sass::Script::Functions
  def strip_unit(value)
    Sass::Script::Number.new(value.value)
  end
end

unitless-messy-example.sass

=unitless-value($property, $value)
  @if unitless($value)
    #{$property}: $value
  @else if unit($value) == px
    #{$property}: $value / 1px
  @else if unit($value) == em
    #{$property}: $value / 1em
  @else
    @warn "I wasn't expecting to find a #{unit($value)} value"
    #{$property}: $value

unitless_clean_example.sass

// sass -r strip_unit.rb unitless_clean_example.sass
div
  foo: strip-unit(10px)