I agree if you don't like the particular birds you have, it's just fine to get new ones. 2-3 years is getting up there as far as egg production goes so productivity will be going down. Keep in mind however, the more time you spend with the birds, the tamer and more used to you they will become. So, if the only reason you're getting rid of them is because they're not tame, I say give it time. Chickens can easily live 6+ years in ideal conditions. However if you're wanting eggs, replace the older birds or get some younger pullets. I start replacing my laying hens when they get to be around 3-4 years old (depending on breed). I sell them as stew hens or we butcher them ourselves and they are replaced with younger birds. But, if are unhappy with the particular birds, like bobbi-j said, there's no sense in wasting your money on feed or your time on something you don't enjoy.