Up to 15 vehicles are believed to have been targeted last weekend as families enjoyed WV1 Fest at the park.
Thieves used circular saws to try and get at catalytic converters.
Two men, aged 52 and 29, were arrested on suspicion of theft from a car and later released on conditional bail as investigations continue.
West Midlands Police has asked anyone who has information including photos or film footage to contact them on live chat at west-midlands.police.uk.
Alternatively Crimestoppers can be contacted anonymously on 0800 555 111.