I personally think it's worth the money for the LED tail lights and turn signals. Our lights are pretty dim and pretty small compared to the blinding brake lights on modern cars so anything that can make them more visible is a good thing.
here on the board makes some of the best LED lights anywhere. His web site's over here: Mustang LEDs
The only thing you need to change wiring wise to switch to LEDs is the flasher relays, and those are simple to swap out. Aside from that the LED lights are plug and play.
For the headlights, even if you're keeping the halogens you should add some relays. It really does make them a lot brighter.
Every time this comes up people are always recommending getting stuff from Daniel Stern Lighting, and he's got H4 bulbs and relay kits so while I don't personally have his Cibie H4 bulbs (yet) I'll go ahead and put the link here. Daniel Stern Lighting Consultancy and Supply
Lights are a nice easy upgrade, they're just not necessarily cheap. But they do make for a more enjoyable drive if you go out after dark.