@mazonemayu
In my opinion the sales during the active life of a console are indicative. Only at this period can a gamer can choose a game of his liking, without issues such as rarity or collectability factoring in.
On the contrary, in the post-mortem world of a console things are too distorted to come to any safe conclusions. New game production supply is limited, mainly 2D, and die-hard fans will buy and play anything with a swirl, whether it be trash or quality, 2D or 3D. Factor-in the collectors that may care more for an enriched collection than a new video-gaming experience. Marvel vs. Capcom 2 might be 5 or 10 times more expensive than Soul Calibur. Would the majority of the community in 2017 prefer a brand new and Dreamcast-exclusive Marvel vs. Capcom or a new Soul Calibur? I personally would bet on the latter.
The DC was and is best known for the games that sold well, which naturally meant they were more popular. The 2D lineup was of high quality, but it was addressed to a small portion of the people. High quality and few copies lead to extravagant prices after production is seized. Your argument regarding the price difference does not stand in my opinion. For the record, I don't count Cannon Spike or Rival Schools as 2D.
My conclusion is that when we are talking about the value of a new Dreamcast game in 2017, for all the technical and economical difficulties that a 3D game poses for a development team, criticism should be much more moderate. If anything, it shows that there is interest still for the Dreamcast and it leaves room for hope for a better release in the future.