This paper focuses on systems development issues (i.e., improvement, extension) for composite (modular) systems. First, systems approaches are considered: (a) improvement of systems components and/or their interconnections, (b) improvement/extension of a system structure, (c) "space" (e.g., geographical) extension of a system as designing an additional system part, and (d) combined system improvement/extension. Communication networks are examined as a basic applied domain. Second, combinatorial optimization models are pointed out as underlying problems: (i) multicrteria ranking, (ii) knapsack-like problems (e.g., multicrtieria multiple choice problem), (iii) clustering, (iv) multicriteria assignemnt/allocation, etc. Numerical examples for communication networks illustrate the suggested approaches.