The matter of volume may depend on the particular classic guitar. A halfway decent classic may not sound as loud as, say, a Martin D-model up close, but believe it or not, a classic has more carrying power than a steel string guitar. I've heard Segovia, Christopher Parkening, Pepe Romero, and others play in fairly sizeable theaters with no amplification whatsoever, and their guitars could be heard loud and clear everywhere in the theater.

I've never had any problems that way with my classics, even when I've used one of my "second" guitars. And I just use my fingernails. If you're not getting much volume, you might want to check your right hand position. And use rest-strokes whenever you can.

Don Firth