I've also been looking at that, and you raise a good point, though I would say the the Promote buff in the utility tree is conspicuously defensive and those should be the ones swapped (besides, it goes hand in hand with the Siege Commander build).
At any rate, it is a valid point that pretty much every jungler wants the gold smite, and every jungler wants extended buff duration. Junglers by default tend to be gankers, even if they're not the initiators in said ganks, so the argument that some junglers can get more gold from ganks is actually not very good, since all junglers get similar gold from ganks; the primary determinant of a successful gank being not the champions, but the execution.
That said, the smite buff should go where any jungler will be able to pick it up, and that is, as the OP correctly identified, the Utility tree, because every jungler wants the extended buff duration that's in there. If a defensive jungler were to go 9/21/0, they're already missing the 20% buff, and it's therefore not a good jungle set up; a defensive jungler will naturally want to go either 0/9/21 or 0/21/9, while an offensive jungler will want to go 21/0/9 or 9/0/21, depending on their priorities and particulars.
I should also point out here a response to the question of "which is better? (gold vs buff)" and the answer is the buff duration of course, but what's important to notice is that this is necessarily true because the buff enhancement is a 3rd tier mastery while the smite enhancement is a 1st tier mastery. If the tiers were equalized (via benefits granted), then the question would be valid; but as it stands, one is comparing chicken pot pies to fillet mignon, rather than a phillips head to a flathead, or an Audi to a BMW.
Now, as for what to swap it with, teleport, flash, clarity, and clairvoyance are all bad options, because those are all either spells that anybody would want (teleport, flash), or spells that mages and supports would want (clarity, clairvoyance) - who will put at least 9 points into the utility tree, most likely.
Promote, on the other hand, particularly with the "conspicuously defensive" buff granted, is not a spell that any fighter or offensive mage (e.g. Annie, Ryze) would generally take. It does however fit nicely within the purview of supports and tanks, particularly pushers. In fact, even pusher/fighters might like it. Whatever the case, pushers and supports will both rely on the defensive tree, at least to a 9-point extent. While pushers may extend into the offensive tree, or the utility tree, they can currently only gain the improved Promote through the utility tree, which means their ability to extend into the offense and defense trees are handicapped, and pushers are in that particular class that really does want to sit between offense and defense.
Supports on the other hand, will almost never care about the offense tree (and if they do, they're probably playing AD soraka, or at least AP carry Sona), so moving promote to the defense tree is perfectly acceptable from their perspective.
There is an alternative option, however, and that is to move Smite back to the offense tree where it really belongs (and ghost, clearly, does not). Whether Smite, Ghost, and Promote all get shifted left, or whether Smite gets swapped with either of them, the options available to players will be greatly improved, without seriously altering game balance except in a way to make things more balanced than they currently are.
[EDIT] I should add, that with the exceptions mentioned, no other class of champions has any difficulty spec'ing for the summoner spells they might legitimately want. It's not as though we're asking for an overpowered or garrishly absurd exchange; but rather one that should be intuitively obvious. In fact, it's a better-than-equal trade, because it's win-win and shores up 2 classes that are singularly denied full access to basic enhancements toward their success in their niche. To not do this simple, intuitive thing would be akin to forcing ranged AD carries to choose between Attack damage and Armor penetration, whereas now they can get both, as well as Attack speed, crit % and damage, bonus damage of all kinds, and still have 9 points left over for whatever they want (including even more damage).