Well, there's a lot of trainers after Rock Tunnel that you fight before you get to Celadon. You can also fight Gary in the Tower and easily grind against his Gyarados and Pigeotto for experience.
I honestly don't think you'll have Pin Missile by the time you fight those Grass type trainers. It learns Pin Missile at Level 48, which is probably around the time of E4. So I guess its good for Exeggutor....and maybe Jynx? I'll test that out when I get there. There's also a traded Electrode that can obtained via trade on Cinnabar Island, has anyone tested that?
Now in Yellow, there is a MASSIVE difference. Jolteon gets Pin Missile earlier, and Voltorb isn't available until Power Plant. So I see it being a tier difference there.
By the way, is doing Cycling Road first the appropriate order? Because if you go by Route order, 13 and 14 lead you to do the Lavender Town -> Fuschia City way instead...if I remember correctly anyway. Then again, whole game is pretty weird when it comes to that stuff.