wat. 6 overseers? does this z just build that many seers blindly?...
I personally hate ghosts. Useless in bw, and still useless in 2. I might get 1-2 in tvp if I see like mass pheonix or some odd mass ht rush build, but every other match up I find them entirely useless. Ghosts aren't cost effective for "sniping" infestors or overseers or anything really. only good for emp. You would have to mass ghosts to keep up with their infestor count, which isn't good. Also, a tech switch would devastate you if you aren't careful with ghost production.
No you don't need a billion Ghosts, but one per every 25 supply or so is fine. Snipe is ridiculous in TvZ, I don't think you understand how great Snipe is. 40 damage, no mitigation, nothing. And even without Snipe they do very good damage against light.
And no Ghosts in TvP? What? What are you going to counter HTs with? Immortals? EMP is a force multiplier and a game changer in TvP. Without it P will beat you each and every time with an equal food count of units, period. EMP is what levels the playing field, and without it you're going to get demolished by immortals (vs mech) or storm (vs bio).
Current TvP metagame is cloaked Ghosts. Protoss literally has no counter. Cloak keeps HTs from using Feedback on them and keeps Observers in check (a quick EMP and a snipe or a round of Marines and it's gone). Ghosts keep Phoenix numbers in check (too many and they become liable to massed Ghost as they're light). EMP cuts 100 shields instantly, that's 200 damage you don't have to deal (shield has an armor of 1) and COMPLETELY shuts down Immortal Hardened Shield/Sentry Guardian Shield. Snipe will pick off very important units like HTs and Sentries allowing your meat and potatoes, your MMM or Marine/Tank army to clean up.
Hell even in TvT Ghosts are great. Nuke baiting forces your opponent to pick his tank lines up and redeploy or face being obliterated, and TvT is ALL about positioning. Clear out cliffs and other choke points of enemy tanks without firing a single shot and make it just that easier to creep up to your oppoent's front door.
Really, try just a couple well positioned tanks. Whenever the z tries to approach with either infestor or banelings/lings, run your bio ball behind the tanks.
That only works until Goldish level where Zergs get enough braincells not to run blings into a tank line.