My first suggestion - shoot it and see what you think. My 2000 model Diana 34 still has the original spring and seal. Power may be down slightly but the reduced recoil usually improves accuracy. Decide what you plan to do with the gun. If you're just killing paper you don't need much power. Synthetic seals don't really dry out.I like to get springs and seals from Air Rifle Headquarters. Be sure to order the correct size for your gun. A properly fitted seal can make all the difference in the world for velocity and accuracy.
You'd have to define what you mean by upgrade. The power can be increased, but only slightly - short of replacing the rifle. Accuracy can be improved by tuning, technique, and the proper pellets.Five shot groups under 3/4" at twenty yards take a bit of practice. With some tweaking and more trigger time you may be able to achieve ten shot groups of a half inch at the same distance.If you can state a specific goal at a given distance you know what you're trying to accomplish. If you're seeking consistently reliable accuracy at fifty or a hundred yards it's probably time to shop for a different gun.