Historically and currently they actually work pretty well until they do break. There's no good reason to replace them if they work.

If the front derailleur is the piston type with the plastic clamping cap, you can get a metal cap to replace teh plastic one - they're pretty common on Ebay. If the front moves ok, that would be the cheapest thing to do. On the other hand, decent all-metal front derailleurs are also on Ebay, usually by the dozens, and prices are pretty low usually.