There is no reason to replace your grill as long as it is working. Here are some ways to make those old Weber grills from malfunctioning.
The first thing that you can do is to give those old Weber grills a good cleaning. If it is not performing like it used to, maybe all it needs is a little bit of washing, as extensive use can clog up some of the components. Actually, you should be giving the movable parts a regular cleaning whether it is old or new. Doing this on a consistent basis (or as set in the manual) will allow the unit to function longer.
Also you can keep those old Weber grills working longer if you buy the right kind of accessories. Of the many utilities available, the most useful would definitely be the covers. Using these you will be able to protect that grill from the effects of wind, rain and too much heat. Although it is true that they can withstand those elements, the effects will accumulate over time. By using the covers you will prolong its life.
Old Weber grills are also better maintained if stored in the right location. This in particular refers to the portables. As much as possible, try to avoid setting the unit in a place where it might get bumped, or fall to the floor. If you are going to take it out camping, do not just throw it in the trunk, but set it in properly. The effects of excessive bumping will not be immediately evident but it will be in the succeeding years.
If some components are no longer working, there are replacement parts for old Weber grills available. Whatever it is you are looking for, be it cooking grates, Flavorizer Bars, handle lights, the hose, you can buy them on the Net. If you want, you can purchase additional utilities to further enhance that old workhorse. Among those that you can buy are work tables, chimney starters, or carts.
Not all of these will be applicable for old Weber grills of course as some are meant for newer models, but there are a lot there that you can use to keep that unit going.
By taking care of those old Weber grills, you will be able to save a lot of money. Instead of buying newer models, you will still be able to whip out those grilled goodies on that old reliable unit.