MilesandPoints,
In order to be eligible for the buy up, you must have previously qualified for a level higher than Bronze (i.e. in 1998 you were either a Silver or a Gold). The program is for members who for some reason did not reach their prior status for 1999. So, Continental selectively sends mailers to members advising them of this program based on miles flown in 1997, average fare paid, etc. Also, you must have flown the actual required mileage in 1997 to reach your status in 1998. If you were bumped up (either via the buy-up or as a courtesy because you were within 500-1000 miles of qualifying), then you are not eligible for the buy up this year.
So, the short answer is that since you qualified for the same level in 1999 as you were in 1998, then there is nothing for you to buy up to.
Regards,
RChavez