The Entity might have still been responsible, but it also isn't the only (or best) explanation.
It certainly isn't the 'only' explanation, sure, but the whole scene had particulars that follow various patterns used in good story telling. Having a discussion about the origins and nature of the portals via the 'entity' and then having a unique portal and opportunity showing itself seems more to reaffirm Robo's theory, rather than suggest any other possibility. While it can be anything else the Chrono crew can pull out of their hat, as it is their product, but without other suitable information present, it would weaken the story telling. There's a particular rule of theater/story telling that comes to mind in regard to conveying information to the audience, and the significance of what is reveled: If you mention *someone* has a gun in Act 1, then that gun needs to go off before Act 3. There is simple importance to what information an author chooses to reveal to the audience, in any medium. If that information can't be trusted, then it either needs to be qualified, or the product is poorly made. Given the high regard given for Chrono Trigger, I claim it is not poorly made, therefore there are patterns of quality story telling that are apart of that quality. Therefore, I think a stable foundation can be indeed be created from the information that was chosen to not only be revealed, but also acted upon.
To note, the Entity is not time. Therefore, Crono may or may not be important to the Entity; Gaspar's statement is referring to something else
Again, from the information granted from the camp scene, which while I do admit they are simply discussing a possibility, but a possibility the has reinforcement in other elements of the game (such as at the end when someone mentions the 'entity' being at peace) there is a connection between the entity and time. The entity isn't Time itself, but it certainly seems to demonstrate a nack for temporal alterations. Furthermore, time is relative, meaning its particular to each being. If being alive is important to you, than wouldn't the means of keeping yourself alive also be important to
your time? Another way of phrasing that is how one chooses to spend their time. What's important to someone, is observable by how they chose to spend their time.
In that context, then Gaspar's statement can be included to mean "Crono is important to Time" period; as in, his significance is more than just defeating Lavos (which I gather from how much weight that put on Crono being revived in multiple endings) and maybe more than just to that planet alone, ie, suggesting that Crono is worthy of a sequel he exists in. Or, the approach can be taken that Crono is important to the time of the entity, ie, the entity's survival, which certainly is threatened by Lavos. Or both in that the 'entity' could be more than just that one planet, and thus Crono could be important to time in the battles against Lavoids, or whatever origin is given there.
Your comparison between the 'entity' and 'life' is a poor analogy. 'Life' is a condition, or quality, a distinguishing trait. The entity is a creature, an existence, capable of actions and decisions. One is capable of deciding for itself was is or isn't important to it, then other isn't.
As for not draining Crono's powers, it doesn't drain anyone else's powers beside Magus's, so we don't really know how that behavior works.
Because Crono intervened on everyone else's behalf. Once you regain control of Crono during that scene, all other characters present are slowly pulled toward Lavos. Considering his purpose in taking DNA and stealing the planet's energy, what else would he do with them by pulling them closer? If he sought to destroy them outright, he would've continued his assault. Either way, Crono stood up and intervened there. If not to save the lives and energies of his teammates,(so they can continue the fight another day) then for what?
