That's a really neat team. I think it's good as it is. DDmence with Fire Blast and CB Aerodactyl and Tyranitar could be scary though. Raikou and opposing Sceptile with HP Fire could possibly sweep after Snorlax is damaged. However, most of these things could be covered by playstyle.
You might want to try Houndoom. It is good to hunt down Celebi and Gengar that would otherwise wall your Sceptile. It 3HKOs Zapdos, and takes out Metagross, Jirachi, and Heracross, things that Magneton can't get rid of and pose problems to Sceptile.
Fire Blast | Pursuit | Will-O-Wisp | Crunch / HP Ice is what I am thinking. Make it Timid and give it > 299 Spd to move before Adamant Salamence. You can invest in a decent amount in Sp Def as well.
Starmie is probably the one to be displaced for Houndoom. However, this opens up your team to more Tyranitar. I'd suggest adding Swampert to not only give your team a solid Rock Resist but also a good DDmence counter and more reinforcement against Flygon and Metagross (just in case Skarm dies).
EQ | Ice Beam | Curse | HP Bug is what I suggest.
This is a good way to lure in Celebi and punish it with HP Bug. It would make switching Houndoom in and then sniping Celebi much easier. Swampert can go over Heracross.
Removing Heracross and Starmie makes your team vulnerable to Fighting Types. Having Celebi over Snorlax can patch this up. It would patch up the CM Raikou problem for one and can provide some nifty support.
There is a few things that it can do. Calm Mind Passing is one, and you have 4 good mons to pass them to. Removing Skarmory with Magneton helps here. I'd give it enough Sp Atk to kill Dugtrio after 1 CM and plenty of HP / Defense to absorb an HP Bug.
Psychic - Reflect - Perish Song is enough to keep last-mon Snorlax at bay and can also deal with Raikou / Jirachi. Perish Song can also put other Celebi into checkmate position with Houndoom if they don't switch out immediately. Persih Song + Spikes helps to wear down the opposing team. Unfortunately, this would have a rougher time taking out Zapdos than CM-Passing Celebi.
I'd also invest a little more in Magneton's Speed, since with that spread you're only tying with Skarmory, allowing it to possibly lay down another layer of Spikes. It doesn't need that much Special Defense to wall resisted special moves anyways.