How does 10+ year old technology compare to modern: Musical Fidelity M1 DAC

My M1-CLIC is still operating perfectly within it's feature limitations (for example internet radio is limited). 

Sound quality is fine: smooth, no digital harshness, applause sounds real, cymbals have tone not just hiss, vocals are sweet and full where appropriate, blah, blah, blah :).

Tangential/hijack question: I’m using an Oppo 105 as a transport/streamer into a Schiit Gungnir. What’s a good DAC upgrade from the Schitt in the $1K range?

@simao Schiit just released a new version Gungnir 2, at $1599 ...I've liked Schiit and Denafrips in that price range, haven't heard the older Gungnir...

How much has DAC technology advanced in the last decade or more?

A lot of significant sonic improvements over the last 8yrs especially in the ~3-8k price range.  

Is my Schiit Modi 3+ better than the Musical Fidelity M1 DAC?

Not familiar with this DAC’s performance 

And secondly: how much can be 'gained' by spending 3-4x times the value of those 2?

It is much harder to sonically differentiate better DACs below 2k as better parts and engineering, in high-end limited niche market, drive up costs.  Whether it’s worth the sonic change/improvement depends on the transparency of the audio chain and the OP’s subjective preferences.