What approach do experts recommend for which additional skills increase market value and role breadth?

Additional skills increase market value and role breadth most robustly when they become visible as connectable signal skills with concrete role and impact relevance. Decision criterion: additional skills must credibly expand profile breadth or responsibility level and must not be formulated as blanket salary promises. Specifically: prioritise additional skills by target role and responsibility level; substantiate each additional skill with a task, tool, or impact. (Sources: ESCO Classification, Cedefop Skills Forecast)