Personally I would go for the lowest price possible and no additional features at all (except the already mentioned improvements) .
There are not a lot of people willing to pay 700 and every additional feature will increase the price even more.
I am not interested in MHL, 4G or any other fancy features. Just give me a solid, bug free and open N900 that has slightly better specs and good battery life.
An improved microsd slot would also be welcome if it will not increase costs.