Although it wasn't intended as an "anniversary", I think what Skyrider eventually became is everything I'd want for a modern anniversary show.
Introduce a new hero, with his own powers, fighting against new enemies, which are related to an older threat... and, at some point, early or giving some breathing room, scale everything up to bring back past heroes, in action. I think the guest appearances should feel like new adventures of those past heroes, and show why people like them. I really liked Stronger's entrance in Skyrider just because it stood out from everything the series had been doing up to that point.
The episode showed several times that someone was spying Skyrider, and, in the end, when he's being utterly defeated - unable to defeat even one of the new monsters and forced to fight against two of them, they had Stronger making his classic speech and entrance. Even though his actor only would return more than 10 episodes later, and the replacement VA didn't really sound like him (compared to say, the voice used for him in Megamax or the modern games), that whole moment just worked very well due to everything there just fitting perfectly for a return of the character.
When Skyrider actually got the actors to appear, I really liked how the past Riders were generally portrayed to be in personal adventures and just happening to meet Skyrider in the middle of them - even if the show was just following Skyrider. Something similar happened in Stronger's final few episodes, where each Rider even got a scene against a new villain before they actually met Stronger.
Decade also seemed to be going with the Riders meeting each other in the middle of each one's stories, but, of course, Decade has the whole issue of most Riders being heavy reimaginations, so their appearances there besides one or two exceptions didn't really feel like "returns", just... introductions.
Now, because Skyrider was never really an "anniversary", outside of the guest appearances themselves and some of the past Riders basically becoming secondary recurring characters (Both Stronger and Rider 2 appear in 8 episodes), there weren't really true references or homages to early shows - not even Tachibana gets a mention, and there weren't minor jokes, cameos or other references calling back to earlier shows, just the Riders back to a new battle against "Neo-Shocker".
Still, if you want me to point at a model that should be used for future crossovers series, Rider or Sentai, I'd just point to Skyrider. The Riders actually being there and showing why they're all heroes, trumps any trivia or other call backs they could throw in.