"would it be appropiate using it in a street engine that will see just a few drag races?"

Absolutely.

"I also need to ask why use your old vavle springs on a new cam break in."

I always recommend this because you never know what valve springs came with the cam if the writer doesn't say in his post. If it is a mild cam and uses pretty much stock strength springs, I would say it might be ok, but you never know when a guy is going to use a set of springs that he got from a buddy that were meant for a 8,500 rpm motor (outer, damper and inner springs) that will wipe all the lube off the lobes during break-in and result in having to tear down and replace everything. If your cam is relatively mild, then the springs are probably pretty mild also, and you skated by.