I will add a caveat to that - the should not depends on what you are using it for. For music listening, which IMO would sort of be the real reason to get the 105, you WOULD use the analog outs.
Given that the enhanced analog section is the main (though not only) difference between the two Oppo players, it would probably be a total waste of money to buy the more expensive one if one were only going to use the HDMI connection.
One can use the HDMI for music listening as well; then, the receiver/processor's digital to analog convertors are used. Either way, the preamp section of the receiver is being used for the audio (because the analog inputs go into its preamp section), so the likelihood of much improvement with the analog with his receiver is small. And he lacks multichannel analog inputs, which makes using just the HDMI even more of a good idea in his case. So I really would strongly advise him against buying the 105, given his equipment. (Of course, he was not planning on buying it anyway.)
For most people, the 105 would be a waste of money. However, it might make sense if one wanted the extra features, or if one had a high end system that lacked the appropriate digital to analog convertors for dealing with the signal coming out of the player. But that does not describe most people.
I agree that via HDMI, you aren't going to see large differences in video and definitely not in audio.
According to Oppo, there is absolutely NO difference in performance between them when using HDMI:
... the BDP-103 and BDP-105 are identical in performance when it comes to audio and video over HDMI ...
OPPO Digital - Knowledge Base
If one is going to use the HDMI only, very likely, buying the 105 will just be a waste of money. The 103 is what I would buy, if I were buying a BD player now.