This generates a very powerful effect. A recurring Mind's Desire effect every upkeep for five mana is not too expensive. The reason it's not playable is not because it's too slow, but because the effect can't be reliably channeled for a host of reasons I won't delve into here.
I think most of us can agree this card's going nowhere, meaning I don't feel so bad about the derail below...
Steve, if the effect could be reliably channeled, what sort of a shell would you build to include this guy? You say that five isn't too much, and that he isn't too slow, so I'm curious to know what this hypothetical deck would be doing that doesn't suffer badly against an early Oath/tinker or running spheres.
That's part of why it can't be effectively channeled: what deck would you put him in? Another is that you'll need enough library manipulation AND big mana spells to consistently flip game winning effects.
This guy generates card and mana advantage, and that's well worth a 5 mana price tag when you get it every turn. That's not the issue.
Evaluating the card through a split between its inherent power and its possible usage is interesting steve.
But when you evaluate the card by itself and say that the effect is not a pb for 5 mana - meaning sufficently powerfull for 5 mana - this is kind of an altered truth.
For

, I would say that the effect itself is a pb.

is too expensive - or too difficult to achieve - for this effect in Vintage.
For

, I would say that the effect is ok to poor (when compared to memory jar, it is very poor). But even if it was ok, then it could be difficult to find the build which could really take advantage of it, given that the classical vintage strategy which can consistently power out a 5 mana artifact - shop - do not play any instants of a sorcery.
For

, I would say that the effect is mediocre, in comparison to other options available (Tezzeret for instance, which can generate card advantage through tutoring, win condition and mana through the untap). And in addition to that, it would be difficult to find a deck to put him in (cause of deck building issue).
For

, I would say that the effect is poor - in comparison to ad nauseam for instance - even if it could be easy to find a deck to put him in.
Let's keep in mind that :
- the effect is only once a turn,
- and the effect only starts the next turn.
If it was possible to chain this effect - as for Magus of the future - then I would agree with you. The effect would be ok, perhaps even good, and then the difficulty would be to find a room for it in an efficent and consistent build.
But here, sorry Steve, but in my humble opinon, first the effect is a huge issue simply because it is weak for 5 mana, especially for

...