Campaign Fusion, or: Parallel Universe Problems

So, this title may be a little misleading on a few fronts, but hopefully, by the end of this you'll understand why I went with the wording I did.

Some of you may recall the campaign I've asked for help on for the past few years, with the bad guy being this guy called The Gentleman, and his merry band of do-badders screwing with the heroes. And you might also remember that this campaign actually took place over several WOTC campaign settings: namely, it started in Greyhawk, then moved to Eberron, and was planned to move to Faerun before it eventually fizzled out. But like I assume any writer must feel like, the fact that people just stopped being able to play didn't mean that the campaign I'd created just stopped forming in my head. Things kept happening, stories kept unfolding, and so now I've recruited a whole new cast of players to see if they can beat The Gentleman.

But, of course, I can't just restart the world - so these guys are coming in about 10 years after the events of the first campaign, and it is here that I'm beginning to have some trouble. See, since the first band of adventurers discovered inter-campaignular travel (for ease, I'm going to call this Sliding, a la the sci-fi show in the 90's) and thus, the bad guys figured it out shortly thereafter, it allows for people to travel to worlds they could have never gone to before, and bring back technologies never dreamed of on their Material Plane. What I start to wonder, though, is with this becoming a slowly more and more understood process, how would the technological diffusion of technologies and ideas happen? My original thoughts on the subject were quite simple: Either the PCs or a bad guy uses something like an Eternal Wand, or a Sceptre, two variations on wands not present in Greyhawk. Another caster sees this, or they take it to an arcane university, or whatever, and suddenly, people are trying to recreate these things. How fast does something like that spread in a world without the Internet?

Now, one friend I had already talked to on this subject had presented the following, in a slightly different direction: You won't get the widespread diffusion of ideas and technologies unless you start importing people. For example: Let's say that some followers of the Silver Flame come to Greyhawk. All of their powers and beliefs are completely foreign, and given the way the Silver Flame people tend to go, they'd probably start going off to try to convert people. Does this mean that the god/demon behind that church now has sway in the Prime Material plane? Does this cause conflict on a deific level? Do people start hunting the Silver Flame folks as heretics?

So this is where I want your thoughts. I'm primarily interested on a technological level, but if you have thoughts on the more intellectual/religious diffusion level and impacts thereof, I'd be glad to hear them too.