I would vaccinate my pets only for things that are deadly and if there is high risk of contacting it in my area. Please do you research before deciding on it.
Some vaccines can shed and infect the soil, you might check if Marek's is the one of those or not. If it is you would have to vaccinate any new bird you want to add to your flock.
Also keep in mind that vaccines are not 100% effective. They are effective but not 100%.
I don't vaccinate my birds or my kids. My dogs only get rabbis vaccine every three years because it is something we have in our area, and don't want to lose them or spread it.