Valencia is the rare large Spanish city that still behaves like a second city. You can book Sagrada-level panic tickets almost nowhere here. The City of Arts looks like a space station and then you ride a bike through a drained riverbed to get there. That combination is the whole appeal.
The money mistakes are almost all food. Paella is a lunch dish from the lagoon villages, cooked in a wide pan for a group, and it is ruined in the old-town plazas that have English menus and photos of mixed-seafood rice. An Albufera trip costs less than two bad tourist dinners and actually includes the landscape the dish comes from.
Where to spend your money
Book: Albufera with lunch, a market food tour, and either Oceanografic or a sunset sail — not both unless you have a spare afternoon.
Skip: hop-on buses (the Turia park bike lane is the transport), extra walking tours after the first, and anything timed around "the Holy Grail in the cathedral" as a two-hour product.
The part nobody tells you
Las Fallas in mid-March is extraordinary and also a sleep-deprivation event. Mascleta firecracker displays happen daily, streets close, and hotels triple. If you are not coming for Fallas, avoid those dates. If you are, book everything — including restaurants in El Palmar — weeks ahead.