The glow plug light not coming on is an indication of one of the following: (the other light not coming on would indicate a flood condition)
1) the glow plug is bad (you've already replaced it with no luck so this isn't your problem
2) your blue wire to your glow plug has a short, you can check this with an ohm meter or by replacing the blue wire, or by trying to use the blue wire to light a lightbulb with a battery or anything that will make sure it isn't shorted.
3) the yellow (ground) wire is either shorted or not properly connected to your engine (check all of the connections and check the wire as stated above for the blue wire)
4) the e-z start unit has a burnt out resistor, this is very common, I have two e-z start units at home that had this issue, you can open them up and replace the resistor if you have a little bit of soldering skill and a radio shack near by, or you can just replace the whole unit.

Try the replacement that traxxas sent you, and let us know if it works, if it doesn't then it is likely a short or bad connection in the blue or yellow wire.

The easiest thing to do is to just go out and get yourself a nice little glow starter, they actually make starting a whole lot easier and they can be left on for a bit during engine warm-up to prevent stalling. It is inconvenient to have to carry another item, but they work a bit better than the easy start for heating plugs.

Ultimatley I prefer a roto-start and glow starter, its more to carry, but it weighs a lot less on the vehicle than the e-z start and a little less than a pull start. Plus it still give you the convenience of an electric start over a pull start. Pull starts are nice if you have your engine tuned right, but they can be a huge pain on a poorly tuned engine.