Cooperation of co-located mobile network operators can provide potential benefits for the capacity expansion without further densification of radio nodes. However, such benefits need to be scrutinised for coexisting cloud radio access network (C-RAN) operators because the inter-operator cooperation may compromise the superb interference coordination capability that each C-RAN has. Furthermore, altering C-RAN infrastructure for the cooperation incurs a high investment cost. In this paper, quantitative gain of inter-operator coordination strategies is evaluated to provide the C-RAN operators with a guideline on their cooperation decisions. The coordination strategies encompass dynamic user association and the spectrum sharing which aim at maximising the total user throughput. A heuristic algorithm is proposed that reduces the computational burden of the coordination significantly. Numerical results suggest that the inter-operator cooperation is beneficial particularly when the network size of each operator tends to be highly asymmetric. It is also verified that the users who belong to smaller network attain more coordination gains.