Training and racing can cause strange things to happen to your body. Things like cramps and soreness are normal, but when you legs turn to stone and you've got new soreness in places you didn't realize contained muscle, your mental state about getting back out and running can be shaken up a bit. Here are a couple of things to consider before throwing in the towel.
Haunting leg spasms I wouldn't worry about those darn leg spasms. Going out too fast can definitely cause them to creep up on you. If you are pushing the pace for too long you can over use those muscles which is a classic case for spasms to hop on board a set of perfectly trained legs. Another couple of reasons could be fluid related or low levels of potassium and calcium.
Extreme weather (hot or cold) coupled with an increase in effort can impact the fluid ratio that you need, meaning drink more if you're going to put the hammer down.
Those sore quads The spasm thing while running is strange, but really isn't that big of a deal. Your quads being sore are likely a byproduct of the extreme contractions your legs were going through coupled with the over compensation you applied to your stride to keep your legs turning over and not morphing into solid rock. Just think of it like if you were lifting weights and contracting your muscles. There is usually soreness afterwards if lifting weights is not something you are accustomed to. In this situation, you're not accustomed to your legs flexing on their own and becoming as hard as bricks. Even one or two tight contractions of the quad can cause this soreness.
So, in summary. Sore quads? Take some ibuprofen and keep on running. You'll be fine.