Should I sell my Oppo 205?

It seems to me that selling an item while it still has value as being a wise move especially if you're not really using it. There's likely few if any spare parts for these Oppo units so if you can get good money for it, then sell and move on.

I had a 205 for two years. Sold it $2k and bought an Innuos Zen 3
which has no DAC but streams, burns & stores. $2.2K.

I also bought a separate DAC. The difference between the Oppo
DAC and the new DAC $1.5k is where the real sound improvement
happened.
The next week with an hour between appts I went in a Goodwill
and bought a BDP 93 Oppo player. Still had the remote $18.

So I can still watch BlueRay movies and listen to DVDs.

Advice to the OP? Keep it. Last of a legacy and you still need it
for the Blue Ray stuff.

But do upgrade your DAC asap.

The real reason to keep it if you no longer play Blue Rays is to use it for a Universal Disc Player. Other than the Sony ubpx800m2, It & its bigger sibling play CD, SACD, DVD Audio & Pure Blue Ray Audio. The Oppos have multi channel analog out so you don't have to use the buggy Hdmi connection. If you don't need the multi-channel out or the Universal disc feature, then sell it. 

I have a cheaper Oppo for Blue Ray and have heard the more expensive units many times. Thought they worked fine as transports and thought that the DAC left much to be desired. Of course now I am almost 100% analog unless I need long play and background music.

If you are using Oppo for playing physical media (like BlueRay or CDs) sell it and buy a very decent BlueRay player for 20% of the money you will fetch. You will not notice the difference and pocket between 1.5-2k U$. However, if you are playing content from the hard drives, DLNA or other streaming sources there is nothing that comes close to Oppo. And I am not talking just about the quality of sound or picture, although that too.

The quality of how Oppo handles network and WiFi connectivity, shared storage, deals with congestion, error-correction and multitude of other things does not exist throughout the industry. After my friend sold his 205, he tried B-ray players from 2 prominent brands. They played blue-discs perfectly fine, with proper Atmos sound and delivered baskets full of 4k goodies. However, none provided Oppo’s quality when used as a network-attached unit. I know it first-hand as I was trying to help him getting things solved. And pretty much nothing we stepped on could be solved. Even though we’ve got long email conversations with manufacturers support. The list is surprisingly long and a subject for a separate post.

I personally own BDP-105 and would only part with it if something like Oppo shows up in the market but so far, nothing on the horizon. Its DAC section can still be considered a reference for audio and I am fine with movies in 1024p. The build quality is great and I anticipate another 5 - 8 years of seamless work.The only thing I regret is I had not catch my friend’s sale of 205 in time...

If you take into consideration quality of build, design and features they were sold for laughingly low price. Those players set up a benchmark that, I am afraid, we will never see again. They also scared the industry sharks to death and created a lot of friction not to say tension in the market. There is really nothing you can compare them to. So, there is a reason 203 and 205 boxes sell far above their shelf-price, 3 years after they were discontinued. People who pay current price do not do it because they feel sentimental. They have far more tangible reasons to do so.