I've been tuning like this for a while now. Definate good increase in mileage. It made me realise that a crisp bottom end that doesn't load up is much more important for good mileage then a (small) restrictor is.
Like you say, watch out for a too small idle gap with this method, it's easy to go below ~0.5mm this way and that will make the bottom end very sensitive & possibly lean.