I was looking at the list of familiars you can obtain with the Improved Familiar feat when I noticed none of them had a stat bonus like the normal familiars did.(Example: The Cat familiar grants "Master gains a +3 bonus on Stealth checks")
Are you sacrificing a feat slot AND the bonuses familiars grant to you to have a better familiar? It isn't a huge blow but it seems that if you sacrifice a feat you shouldn't lose a bonus that is given as a base ability.