I got the Prima Strat guide for $10 on sale last week. Figured what the hell. After looking it over for 5 minutes, I felt ripped off. It blows. Only thing interesting was the CS maps from overhead. I just got into CS recently and still don't know the maps all that well.
I got Silver and don't regret it. I had only played HL1 for roughly an hour about 3 years ago. Never went back to it for some reason. So, I actually started HL:S last night and I'm enjoying it. Graphics aren't improved or anything, but I think it's great fun. Plus, I have some friends that still play regular CS because their comps aren't all very good.
Really, it comes down to what you want to play. If it's just HL2 and CS:S, Bronze. If you think you might play HL1 again or want to try out some of the mods in the back catalog, spend the extra $10. Heck, it's only $10.