Sonic differences, no.
I compared the Apple Dongle against an ifI Go Bar, Gryphon, Diablo and a Chord Mojo and with IEM where the power output isn't an issue I certainly didn't hear any really obvious difference and certainly nothing that would come close to justifying the around 50 - 100 times price difference !
EDITED TO ADD: IEMs were Shanling ME700 and MG600, Letshuoer S12 planar and Dethonray Tender 1 planar.
In fact, using the Tender 1 which are a very power hungry planar IEM I was comparing the Apple Dongle to an ifI Diablo while working from my home office. I got disturbed by some work stuff and after a few emails etc to sort things out I thought about the music I was listening to in the meantime. I thought to myself that the Diablo sounded great only to look down and see I was plugged into the Apple Dongle !
I have been told that there are simply some people that physiologically don't hear the differences that DACs and Amps can make but I figure if I can't tell the difference between a $10 Apple Dongle and a $1,000 Diablo the differences that others might hear have to be subtle and a long way from the dramatic differences that some would suggest.
I look at it like this. The Apple Dongle is a cheap little accessory so it is looked down on by many. BUT, it has been made in the millions, so the development costs are a negligible part of the price and it was developed by the engineers of one of the biggest tech companies in the world. Why would Apple not be able to put together a nice clean sounding, good performing little DAC ? They have massive resources, a huge pool of highly skilled technical people and would have a massive budgetary and resourcing advantage over any audio specific company in existence. Why wouldn't it be decent ?