There is no need to replace items still working.
I don't clean my flavorizer bars, I just move them around occasionally from burner to burner so they burn-off evenly.
@Chris Allingham has an
excellent video on cleaning grates: You could de-gunk the lower deflectors with oven cleaner too.
The flavorizer bars and lower deflectors don't last forever, but I only replace them when they rust apart and flames start to lick around the edges.
Since the burners are protected by the flav bars, if they are in good shape they may just need a little cleaning. I would remove the grates and flav bars, light all burners and look at the flame. If it is even, and blue across all burners don't touch it just keep cooking.
If you do need to buy flavorizer bars, if you can find 16 gauge stainless they will last a long, long, long time. I haven't shopped for these in a while but there are a couple of suppliers that have 16 gauge. Some on amazon are 17 gauge, some 18, some 20. I put a set of 17g in a friends E330 and it does well.
The other item to look after is the heat shield on the left hand side. These tend to take a lot of abuse and rust away. I'm going to make my own replacement ( some day ).