you see the tallest pylon in the UK (just don't sit under it as you set off the alarms and a nice man in a 4x4 rolls up to tell you off!).
just googled it; a base jumper managed to kill himself by trying to parachute off one off the platforms (chute didn't open not zapped by 400Kv) so not surprised it's high security.
If the Kent and Essex ends were anywhere near the TFL zone 6 it would be worth doing on a day Travelcard but otherwise an expensive exercise.
I did get the train out to Tilbury and back from Gravesend in the 1980s, the ferry had a BR double arrow (reversed on one side of the funnel, the only place you see this now is on our local bus to Gatwick on the map along the inside)
Anorak
the Gravesend ferry terminal also had its own station with a branch line from Longfield, a short section was reopened in order for Eurostars to get onto HS1 from Waterloo before SPI opened, they can't anymore because they only run on 25kv AC
/Anorak
At the time Tilbury had a proper old terminal with its own station, it's still there although not sure if used by anything