Agree - my only ever experience of proper rivalry was the Maidstone derbies of the early 90s and Swindon in the mid 80s. We genuinely hated both clubs and they hated us.
The Swindon rivalry fizzled out 30 years ago from both sides, even if some try to keep it going - the numbers we take to Swindon and them to us and general lack of animosity between fans at matches speaks volumes - it's just another game now.
However, were we to play Maidstone (and to a lesser extent Dover and Ebbsfleet), there would definitely be a local rivalry. It would be there from the off from them due to their lowly nature, but could really develop to something tasty and mutual if any of them stayed in the League, especially if we had an extended spell in the same division.
I remember being at school in the early 90s and the Gills v Stones games were the first time I felt we ever had a proper local rival (especially with them having Lord Sir Keith as boss and half of our old team) - it was like what we saw third hand with Merseyside, London and Manchester rivalries on a smaller scale (real fans in those cities of course, not gloryhunters down the pub!) There were only a handful of Gills and Stones fans at my school, but come derby day, even those who didn't support either team (and at best ignored the Gills or Maidstone for the rest of the season and, at worst, ridiculed them) had a team and passionately followed them for the week or so before and after the match and got involved in ding dongs. It was sadly short-lived as funny as Maidstone's demise crassly seemed to a teenage Gills' fan at the time!
Bring the derbies back I say. Given the way Ebbsfleet are investing and Dover have done in recent times, and the state of our management team and squad, I can quite possibly see a Kent League Two derby in a year or two.