Oh come on, you need at least one not-terrible way to produce power mid-game.
I'm not actually sure I ever disabled tesseracts anyway, or if I did I didn't do it properly. In practice the inability to generate efficient power teleportation is the biggest problem you'll have with them. Besides all that, they're excellent lag reducers and that trumps other concerns for me these days.
*mourns my server's consistent 15TPS tick rate*
For Nuclear Reactors, after personal experience with them I have come to the conclusion that their default balance is sensible for vanilla IC2 but pathetically terrible for GregTech installations. Nevermind that it's technically possible to get nukes that match a fusion reactor for performance, good luck actually getting anywhere near that in practice. With that in mind, they're now balanced in the pack to be a worthwhile alternative to solar power.
Something has to be, jeez. XD