Plus, unlike Kamen Rider, where each world has a unique feel that stretches past suits, weapons, mecha, you can pretty much do all 34 worlds without putting as much work into the writing (see: Decade) and turn out okay.
I think it's kind of ridiculous to argue that Super Sentai as a franchise lacks shows with a distinct feel. It would completely suck if Goukaiger shot and wrote its Bioman episode in the same style as, say, its Carranger episode. It would be completely inappropriate, offensive to fans, and probably very confusing to kids who are just learning about these older teams.
Even just in the past ten years, could you possibly write a Magiranger homage episode in the same style as a Dekaranger homage? Or a Shinkenger homage in the same style as a Hurricanger homage? That wouldn't even begin to make any sense. That would flat-out nullify the point of even mentioning the older teams.
Super Sentai isn't willing to break its formula
completely in certain years the way Kamen Rider is, but a lot of Super Sentai seasons still have very distinct stylistic approaches. You don't necessarily need the original actors or production teams on board to recognize that, but it does need to be recognized.
And yes, getting original actors to return would vastly strengthen the crossover concept. The Black/RX episodes of Decade are by far the most memorable, because they're the only time Tsukasa interacts with a character who is not, for all intents and purposes, just a new guy wearing an old suit.
Now, poorer Super Sentai seasons do tend to feel bland. I don't envy the guy who has to write episodes lionizing the likes of Fiveman. But frankly, I think those shows are the exception that proves the rule. Most Super Sentai shows have some obvious gimmick of concept or style that can be easily homaged even if they can't get any original actors back.
