I am kinda old school. I am used to brushed motor technology. I have been working on my driving and getting a couple of decent vehicles together to race.

Currently I run:
1. Associated B3 buggy with a brushed 11x2 with Lipo 5000 20c
2. Losi Strike SC with Castle Sidewinder 4600 with lipo 30c

I am kinda intermediate with little race experiece. the place I race at now doesn't have motor or battery limitations but I want a setup that will be able to race anywhere. At least with extra parts on hand.

I'm thinking that the buggy needs a brushless setup. I don't know how the sidewinder fits into the roar rules or what motor I can run to make it legal. Beyond all that I am lusting after a better kit for my SC. What would you do? What classes would you run?

I'd recommend attempting to run what you currently have in the Buggy and SC classes available at your local track and have fun racing RC! If interested in upgrading electronics, there are many top name brand packages to consider. I chose Tekin ESC's www.teamtekin.com and Murfdogg Synergy Motors www.murfdogg.com, for their outstanding performance, reliability and unsurpassed customer service. You would be pleased with any of the current brands available, as technology has advanced alot since the brushed days. Hope this assists you with your futrue decisions in elec packages and RC endevors!

GO RACE!!! lol you won't know what you really need until your in the situation. Most of the time guys who race are very helpful and will offer you tips. Also if you go practice talk to the fast guys ask them about tire choice tires are a huge part of your game. Along with suspension setups

i'd throw the sidewinder in the buggy and try to sell the strike. just race one class until you get used to how your track runs things. upgrade your kits along the way and eventually add to the stable. i started out racing a brushed rustler with nimh (not for long ) and now have a blitz, b4.1, and hopped up T4 all with brushless systems on lipo.

What are you looking for in the SC area? Your 4600kv is close to the max KV recommended for a SC truck.

Pay attention to the lines that the faster racers run. You can learn more about racing by watching, and paying attention to the small details than anything. Try to learn what adjusments they make, and why.....rather than do what they do. Their driving style is different than yours, so what works for them might not work for you. Make one adjusment at a time. If you wreck in the same spot twice your going too fast......I could go on forever. Watch you temps, go as fast as you can, dont wreck, be the best corner marshall that you can be, have extra a-arms, and the best tires you can run!

buy a transponder

Go to your local track and see which classes are popular. Pick one. Then focus on just that one class. Try not to use a bunch of aluminum for a racer. Use RPM's plastics if they are breaking on you. Also get the transponder like liver said.

good advice

I wouldn't race either of those. Problem is your not going to find anyone else racing either of those vehicles so its going to be hard to get setup advice, and parts if you break them. No reason to start with an un-needed handicap.
If you want an easy and affordable way to get into racing, pick up a RTR Brushless SC10. You could also go RTR brushless B4 if you would rather race buggy, but the SC10 is easier to learn to drive fast on a track then the buggy will be.