Is there parking at the marina?
Yes at the main marinas, and it is usually a small paid car park. Boca de Tomatlán is the exception and is tight, so arrive early or take a taxi.
Marina Vallarta, Nuevo Vallarta and La Cruz all have parking near the docks for a modest daily charge, payable in cash. Boca de Tomatlán has very limited space and fills early, so a taxi is often the easier answer there.