Although the classics have a history of safe use, and as such, as proven safe, you also have to remember that "RC" is not a type of drug. LSD and MDMA used to be "RCs". The stuff in Shulgin's works (PIHKAL and TIHKAL) are all closely related to the classics. Some of them have been used by humans since the 60s and 70s. 2C-B is an example, it's been a fairly popular drug since he 70s/80s and there are no cases of problems that I'm aware of. There are some to watch out for, like the NBOMes. But there are some fantastic psychedelics that rank right up there with the classics. Some of my favorites:
2C-E - Hands down the most intensely psychedelic substance I've ever consumed. It's in a league of its own
DOC - Kind of similar to LSD but different in a beautiful way
AMT - Has just as long a history of use as LSD. It's like a cross between LSD and MDMA sort of, but not like a candyflip. I prefer it to MDMA.
Any of the 2C-X series pretty much is great. Any tryptamine (unsubstituted, 4 substituted, also I like most 5 substituted ones but some people don't) are great drugs.
There's a whole world of psychedelics out there. That said, LSD has it all, and mushrooms have given me the most profound experience of my life (actually 2C-E ties it, but in a totally different way). You don't NEED to venture out, but if you're the exploratory type like many of us here, there are a ton of worthwhile substances to investigate. Some purists think that only the classics are worthwhile, but they should remember that both LSD and MDMA are synthetic and were only discovered and popularized by random chance. If things had gone differently, they could both be "RCs" right now and, say, 2C-E could be the gold standard that everyone measures everything by (and it could be, let me tell you).