I'm also a great fan of Revell acrylic paints - they brush and spray extremely well, and since last year Revell have expanded the range of colours a lot (I still use Games Workshop and Vallejo for metallics, though; I find Revell metallic acrylics aren't much good for fine detail work, though their Silver and Aluminium are good for large areas, e.g an aircraft in "natural metal" finish)
However, I'd definitely recommend varnishing the hull of a working model if painted with acrylics. The paint is waterproof, but isn't as durable as enamel, so you will get scratches and wear. A coat of enamel varnish is ideal as it's not only durable but also slightly water-repellent, being oil based.