Electronic triggers are a whole lot more than a way of getting full auto (both Race and Eblades are, or can be set, to tournament-legal semi-only mode - otherwise nobody would ever be allowed them on the field!)
An electronic trigger is so much lighter than a mechanical trigger which makes it easy to "walk" with two fingers, thus letting you shoot fast (try shooting 15bps with a mechanical trigger!) Because of the lighter trigger pull it is easier to keep on target when shooting, or to shoot accurately when walking or running. If you have some money to spend, an electronic frame is an essential upgrade to any cocker these days if you want to be competative.
Electronic frames stop working when then battery dies. A possible downside, but if you keep it in mind it shouldn't ever be a problem. Race frames have a rechargeable battery which lasts for days of play at a time, and comes with a charger. Eblades take normal 9V batteries (does the E2 have a rechargable?), and although the Eblade has a reputation for eating batteries, if you remember to replace the battery regularly it's not a problem.
Hinge triggers are still mechanical, thus still relatively long and stiff trigger pull, but most people find them much better than normal slide cocker triggers. Hinge triggers are, as the name implies, pivoted at a single point above the trigger, instead of sliding in its housing. This makes double-finger triggers possible. They are very easy to pick up cheaply now, though, especially since so many people are selling theirs off to replace them with electronic frames.
As for other upgrades, which is the best depends on who you ask! The Nexus upgrade kit is certainly up there with the best, although many of the parts are Belsales (makers of the Evo) parts with different milling.
Hope that all helps a bit
