Some groups allow verts, but BMWCCA events do not. Personally I think it would be nuts to take a convertible to a track, either soft or hard top, without a cage. Just not worth the risk. One of the reasons why I went from an E46 M3 vert to my E90.
08 E90 | Jet Black / Black | 6MT
Mods: RAC RG63 w/ Pirelli Corsa 255F/285R | Akrapovic Evo Exhaust | OEM Blacklines
Winter Setup: OEM 18s w/ Nokian Hakkapeliita R 245/40-18