[Kuruharan]

Can anything good come from anyone else?
Nothing much happened with the elves that refused the summons, and the more the elves followed the Valar, the greater they became. For example, the Teleri learned shipbuilding and those sorts of things from them, while the Noldor went to Valinor and it was there that they learnt most of what they knew. When they returned, they spread their knowledge.

True, but the Avari never were associated, as Men were, with immediately falling into evil when they were left to their own devices. Elves on the whole seem to have an innate instinct to the good that Men lacked. Ex. The Elves fled from Melkor and feared him in their earliest days while Men worshiped him.

Even though their homes for long years were in Rhovanion, relatively near large settlements of Silvan Elves in Mirkwood and Lórien, they seem to have had little contact with them and instead regarded them with fear and awe.

The Rohirrim and related peoples had extensive contact with the dwarves in their past, though.

but people like the Breelanders seemed still good.

Now the Breelanders are an interesting study because they were of Dunnish stock way back in their day. The Dunlanders are explicitly mentioned as fearing and shunning the elves and being shunned by them in turn.

I suppose the long years of being in Arnor may have wrought the change in them.