Is table really more importsnt than cartridge?

Rich, If you want practical, my sugestion would be that you do nothing at this point in time. Spend some time learning about turntable/arm/cartridge interface before you do anything or your likely to be flushing your $300 down the drain. You have to learn how to match the arm to the table and the cartridge to the arm and then match the cartridge to the phono preamp to maximize performance. Screw up one of these items and you're nowhere. FWIW, the place to start the process is with the turntable, otherwise you are building your house on sand (so the saying goes).

Raul, IF you have a good turntable and the arm you have attached to it is properly matched to the type of turntable you have selected, even though the arm and turntable are not of the highest quality, then I would agree with you that changing the cartridge would give you the most apparent change in the system.
However, for some one with a turntable/arm/cartridge who wants to improve what they are hearing its not that simple. Tonearms and turntables are not all interchangeable - the design criteria of each narrows down the possible choices. Some arms work better on suspended tables, some better of unsuspended tables. Of the tonearms that can be used on suspended tables one has to be sure that the weight of the arm is within the capacity of the spring suspension otherwise you will never get a good set up. The same can be said for cartridges and tonearms. Its all about matching tone arm mass and cartridge compliance. And as to the phono pre, its all about selecting the one which can deal with resistence or compliance issues presented by the cartridge. Ditto I/C's. To change any single one of the basic components requires some research to get it done right. Thats why I recommended that the poster do some reading on the subject.
In passing, I find it interesting that the poster never stated what he found objectionable about his present system, just that he wanted to improve it. Personally, I don't think he will get the improvement he is seeking by just changing his cartridge (which is a fairly good cartridge), in the dark so to speak, unless he can articulate how he wants to improve his system and what he finds lacking in his present set up.

Winegasman, Actually the art of making turntables has progessed markedly since the days when the Duals, Thorens, whatever, ruled the market. I won't list all of the possibilities, however a couple of the big ones are the removal of the motor from the plinth and the use of a platter with substantial mass to control rotational stability. If you are seriously interested in upgrading your rig, I would start from scratch, or as a reasonable compromise assuming that you have normal budget concerns, buy a modern table that is already set up with an arm. I'm very partial to the principals being used by Nottingham and they have such a table which costs about $1000 (last I heard) including arm, called the Horizon. Add a cartridge and then you can start thinking about diminishing returns from high priced rigs. There is nothing wrong with what you have now, and its apparently serving you well. As I said earlier, save your $300 and, if you are serious, read about whats possible and then decide how its best for you to proceed.