If you play advantage, you are saying that there is still a promising attack
No, you are not saying that - neither based on what the Laws say, nor on logic. As per the Laws, the referee is simply saying he believes that by allowing play to continue, "the non-offending team will benefit from the advantage." Note the use of the future tense - the whole point of advantage is that the referee doesn't know yet, what will happen and is allowing time to see whether the team will eventually benefit (usually in the form of a promising attack) - or not.
Just because this is what the referee believes and hopes will happen, it doesn't mean that after attempting to allow the advantage, a promising attack will not ultimately be stopped.
therefore you cannot issue a caution for SPA. The same goes for DOGSO. This comes from FIFA.
The Law continues by saying that the referee "penalises the infringement or offence if the anticipated advantage does not ensue at that time or within a few seconds." Which means that even though the referee might have thought that that a promising attack would develop from the advantage, if it does not they can still go back and punish the original offence. If the original offence turns out to be one that ultimately prevented a promising attack, precisely because the advantage did not ensue, then the player can still be cautioned.
I have never come across anything from FIFA - or, more to the point,from the IFAB, saying that you cannot go back to caution a player after an advantage has failed to accrue. If you have such a ruling or recommendation, I'd be most interested to see it.
In fact the Laws say more or less the opposite, that "if the referee plays the advantage for an offence for which a caution [...] would have been issued had play been stopped, this caution [...] must be issued when the ball is next out of play". In the scenario we're talking about, the time when the ball is next out of play is when the referee stops play to go back to penalise the original offence.