If you only keep the TCH one year then you'd probably lose 2/3 of the tax credit. Even if the TCH holds its value well it never pays to trade a 1 year old car. Especially if you pay MSRP and then next year when production catches up on the TCH and they possibly start discounting them. That would hurt the 1 year resale value.

If I knew for sure I was going back to a convertible I'd figure out what I wanted and get it now.

To specifically answer your question, if you get a $31000 TCH and next year (this is already a 2007 model) they discount them $1500 that year I don't imagine you'd be able to sell it for more than $24,000 (and trade for say $21,000).

With my tax credits I'm only going to have $24,000 in my loaded one ($2600 Fed and $3750 State tax credits) so I would have a hard time paying big dollars next year for a used one unless I simply couldn't find one. I really believe they will be plentyful in the summer of 2007.