Agreed- Santa Cruz is awesome. I got a Blur when they first came out in '03 and have ridden the piss out of that thing. Still an awesome bike- far from obsolete. I wanted to try a 29er though so now I'm on a Tallboy.
For riding both on and off road, if you want any kind of decent performance, get a dedicated road and mountain bike. The next best solution is a mountain bike with a seperate set of wheels for road tires though. By the time you get wheels, tires, rotors, skewers, and a cassette though, it's usually cheaper just to get an inexpensive 8 year old entry level road bike, and that'll give you much better performance.
I wouldn't bother with incrimental upgrades at Sports Authority. If you want to get into riding, get the best bike you can justify. Ride the hell out of it until it's worn out, or until you want to do a SIGNIFICANT upgrade. All of my bikes have been 50-120% more expensive than the ones they replaced. If they weren't...just keep riding what you have until it's worn out.
For a winter glove, I like Castelli, but there are a lot of good choices out there, including whatever you have lying around in a pinch.
Regarding your crash- I think a lot of beginners treat a bike like a car...sit on it...jam on the controls...hit stuff. Really, a bike is a lot closer to a pair of skis, skates, or even a pair of shoes than a car or motorcycle. You really have to feel what it's doing through your feet and adjust how much weight you put on each wheel, adjust your cg fore and aft for maximum stability and traction depending on how hard you're braking or how steep you're climbing, etc. Really relax and let the bike float over the terrein. Don't panic in a skid. Relax, feel the balance, and ride it out. You may want to practice skidding in a gravel lot.
Imagine running towards a curb. You just don't run right at it, crash into it with your feet, and brace for impact. At the instant your feet would hit the curb you bend your knees to pull your feet up and set them gently down on top of it, then extend your knees to stand up. It's the same on a bike.
Same with braking. When you run and need to stop really fast, you don't just stop your feet- you lean back first. If you're on a slippery surface and your shoes start to skid you just have to feel what's happening and adjust your balance accordingly.
Also...cornering; during low speed cornering you just turn the bar the direction you want to go, but when you go fast cornering is mostly done by leaning. It's in the knees, feet, and hips. Put your outside pedal down, put your weight on your pedals, and point your knees and hips the direction you want to go.