I think the biggest mistake with Spelljammer was focusing on the "connective tissue" aspect as opposed to the setting in itself (a mistake they did not repeat with Planescape down the line). A large part of the core box focused on "taking your campaign into space" and how Greyspace, Krynnspace, and Realmspace looked, and a lot of the source material built upon those settings (tinker gnomes, ship types used by the Red Wizards as well as Kara-Tur nations, well-known Spelljamming harbors of Toril, and so on). This sent the message "Hey! You want to have your GH campaign take a trip to Calimshan? Well, here's how!"
I don't think providing more options in this way is a mistake. The great thing about this kind of option, is that you can set your Spelljammer campaign somewhere else in the theoretically infinite Phlogiston, and use all of the Spelljammer material with none of the other settings. Or, you can play your Spelljammer in the areas that are close enough for the other settings to be accessible. It's a whole universe of freedom. The focus is up to the group, as it should be.
Realistically, and I use that word loosely, the need for interplanetary or interstellar travel between two or more fully-developed settings should be rather miniscule. After all, both Greyhawk and FR were designed to stand on their own, with little need for contact with each other (except for various archmages sitting down for dinner at casa Greenwood).
Need in what sense? We're talking about what people enjoy. I was just saying to some friends how I think Christmas trees ought to be gaudy rather than elegant. Should I be told, "Christmas trees don't need to be gaudy. You can get your colored lights on the house, etc, etc, and all you need are white lights and subdued ornaments for an elegant tree"?
I
want' my Spelljammer as an (optionally) connecting tissue, since my campaigns are often set in "the multiverse."
And if you have orbital transport, why would the Zhentarim be so hell-bent on finding a path where they can cross Anauroch?
The original boxed set had a pretty strong attitude that groundlings didn't know about spelljamming. The only ones who tended to know about it were a high ranking government official or two in
some governments. If I recall correctly, the elves of Evermeet had like one advisor to the monarch who was in charge of diplomatic relations with the elven imperial armada, and even the rest of the government didn't really know what exactly that was all about. Think of that scene from Independence Day when they President gets told that, actually, there are aliens.
Later products (as they often seem to) screwed that up and made spelljamming tie ins bigger and more well known.
Like Dark Sun and others, the original flavor was the best.
A Star Wars-y approach to planets works a lot better for gaming purposes: this here is the Ice planet, that's the Jungle planet, that's the Desert planet, and so on. But that's hard to pull off if you already have "the Everything planet". I maintain that the default for the setting should have been something like the Astromundi Cluster, except perhaps stretching across multiple crystal spheres. For those who don't know: the Astromundi Cluster was a crystal sphere where many of the planets had been shattered in some ancient catastrophy, leaving a bunch of asteroid belts all over the place instead. Since each asteroid is rarely self-sufficient, spelljamming travel between them was fairly common.
I think that works extremely well. I even would be fine with it presented as the primary focus in new Spelljammer material. What I wouldn't want is the connection elements to be entirely left out. They need to be there as an option.
I just never saw the point in having Spelljammer as a setting connector when you already have planar travel for that purpose. Sure, plane shift is a pretty high-level spell - the price suggestions in the DMG just gives it a non-helpful "usually only cast for those of a similar faith, and even then a special service is required." Comparing it to spells of similar level, you have true seeing costing 5,000 gp.
But using the Spelljammer rules, if you wanted to go from Oerth to Toril, it would take 80 days to reach Greyspace's crystal sphere, 2-20 days to find a portal, another 10-100 days to reach Realmspace, 2-20 days to find a portal to get inside, and then 30-34 days to reach Toril. That's about half a year, about four months of which is spent in a moderately risky place (Wildspace), and which requires an investment of at least 120,000 gp (100k for a minor helm plus the cost of a useful ship) or so, plus the cost of a handful of crew (including at least one spellcaster - preferably two - in order to run the helm). If you have a powerful enough mage, they can create their own portal through the crystal sphere, but that's a 5th level spell - the same as plane shift (albeit a wizard instead of a priest spell).
Or you could get a cleric to cast one 5th level spell. Or perhaps find the right portal.
I'd change the prices a bit on some of the spelljamming stuff, taking the 5e suggested magic item costs in mind (actually, I inflate those costs, so perhaps the spelljamming prices are right for my needs as it).
And the travel times are a bit rough. I think I'd probably quadruple spelljamming speed in the outer planetary areas of the crystal spheres. Once you get far enough from the primary, arcane space becomes faster to travel in. Works well on the map too, because then you can traverse a single square in a day, rather than taking 4 days to do it.
But you are entirely correct there. Whether you are using it as connection or as a setting of its own, it needs to be understood that it most definitely is not
just a connector. There are a bunch of people (I use that term loosely) that live there. Some of those people have ships, so everyone needs to have ships for self-defense. Some of those people use ships to transport cargo, so pirates go after it, etc.
I agree with your logistical and thematic observations, I just think it is extremely important that any new product that comes out makes sure to provide an option for using Spelljammer as a way to connect published worlds. (I use it as both its own setting and a connecter in my multiverse). Not doing so would be a mistake, and conflict with 5e's general inclusivity of D&D history.
