I would advise against accepting Athenian offer, yes we will gain more money and what some consider to be more leverage on Athens as exporter of Grain to them,but what kind of leverage we have if Athens can always turn towards bosphorus if they feel like it.
But let's see what we will loose, QM himself confirmed that Taras would be ready to embark towards closer relationship with Eretria so alliance with Taras would be possible followed by them joining our league, which would make our goal of Italian Leauge closer to reality.
On other hand Athens won't instantly cut all its ties to us, they will be offended but they will not attack us over it and will continue to have good relationship with us.
Basically any deal with Athens is with temporary gains for us, but at the price of prestige and political loss in Italy as Leauge that we wish for would be out of our grasp.
If we become the Athenian main source for grain they certainly can't simply turn to the Bosphorus whenever they like it. Establishing such massive trade-routes takes time and effort and isn't something easily done.
And why exactly do you think that we would be able to mollify Athens but not Taras? I mean sure our southern neighbour will be unhappy about that declartation of friendship, though I think it is important to remember that while we may go against the spirit of our agreement we keep to the letter of it, but just as we should be able to hopefully to negate the negative effects of rejecting the treaty we should be able to negate the effects of accepting it as well.
Also I think it is a bit overdramatic to act like this treaty would bind us to Athens, sure Alkibades might have devious plans and Sparta and Co won't be that happy but it would be a first step in getting involved in the conflict and nothing more. There are almost certainly to be opportunities to draw back, especially if another faction in either Eretria or Athens takes power. And honestly if Sparta doesn't want us to join Athens it is time they start to
bribe convince us, I mean what good is being a neutral and important power in a war if you don't get sucked up by both powers?
And I would argue that accepting such a treaty doesn't necessarily damage our prestige or political influence, indeed while it might hurt our trustworthiness to some degree having a positive relationship and hopefully the support of Athens behind us should if anything further our influence and reach. Especially with those poleis who are also favourably inclined towards Athens like Thurii.
And while I personally would have nothing against Taras joining our league in some manner (though I don't see that happening anytime soon and without major reforms on both sides considering how unwilling most greeks are to give up their independence) I would however argue that such an event would make an Italian League, at least one that includes us, less likely instead. The most likely reaction to such a powerful faction forming would be for cities like Thurii, Metapontion and Co to form their own alliance to oppose us and Rhegion and in all likelihood reach out to Athens/Sparta or even Sicily for support.
Honestly considering that thanks to our decision to let Rhegion wage war on Lokri the local balance of power got demolished and most of the local powers are more likely to wage war upon each other than anything else I have to say that dreams of an Italian league seem pretty far stretched and I would argue that a closer relationship with Athens is the least of our worries there.
The key to an real Italoite league isn't Taras but Thurii and Metapontion (and if you get ambitious Rhegion), if you get those two to really ally with us or join us in a more permanent political union Taras will have very little chance then to go with it unless it gets massive support from mainland greece/elsewhere.
