Having just gone through this dilemma, I seriously thought about going back to a zed, with discounts up to £14k on a 35is it is relatively cheap motoring. However, for me the design is now 6 years on, that is a generation in terms of cars and things have moved on. I test drove the M235i convertible and it is mighty fine to drive and obtained £5k off list from BMW York, have to say it handles very well, steering has significantly improved on the e89 which was one of it's disappointments. The thing that got me with M235i was that it doesnt look like a £40k car and it just didn't float my boat aesthetically speaking.
While I was waiting comfortably for Dan@York to get my figures, I just kept looking at the Estoril blue/red leather 4 series convertible that was close by and thought that's so much nicer.....I was sold