How robust is the system needing to be?
A Geo Metro cant perform as a Power Stroke Ford F-350 can with how much it can carry and how fast it can move. If you are expecting the system to not to be strained or have to carry to much data then go with something that will perform like the Geo, but if you are expecting high volume and a lot of strain then go with the F-350.
Will it work with the existing system?
Lets continue to think of the database as a car and now your system as the garage. Can your new car fit in your old garage? Or are you going to have to build a new garage for your new car? You need to make sure that what you already have in place is compatible with what you are going to implement.
What will the cost benefit be?
If its going to cost to much to keep the system up and hire someone to maintain the system then it may not be in your best interest to upgrade to a new system. However if you are able to do most of the work yourself, find forums, and other useful tools that are free then it could be beneficial to you to implement the system.
Keep these three questions in mind when you are thinking about upgrading or starting out with a new database.