The disclosed technology provides improved compositions and methods for dispersion and drying of nanocellulose, for polymer composites and other systems. Some variations provide a nanocellulose-dispersion concentrate comprising nanocellulose and a dispersion/drying agent selected for compatibility with the nanocellulose and with the nanocellulose-containing composite product, wherein the dispersion/drying agent is selected from the group consisting of waxes, polyolefins, olefin-maleic anhydride copolymers, olefin-acrylic acid copolymers, polyols, fatty acids, fatty alcohols, polyol-glyceride esters, polydimethylsiloxanes, polydimethylsiloxane-alkyl esters, polyacrylamides, starches, cellulose derivatives, particulates, and combinations or reaction products thereof, and wherein the nanocellulose-dispersion concentrate is in solid form (e.g., a powder) or liquid form. Other variations provide a nanocellulose-dispersion masterbatch (e.g., pellets) comprising the nanocellulose-dispersion concentrate and a carrier material. Other variations provide a nanocellulose-containing composite including the nanocellulose-dispersion masterbatch or concentrate and a matrix material. Processes of making and using the disclosed compositions are described.