My ideas about sprites vs. 3d models
First of all...I've had allot of experience working with 3d models and I've found that they are not only easier to work with than sprites, they look cleaner too.
On the subject of whether they should be used in SRB2 or not, leave that up to the people who made the game. If they wanted to use them, they would. Just be glad they did what they did. A good 3d home brew of anything is very hard to find, mostly because it's hard to do with what's available for home brew construction.
Besides, the sprites help maintain the cartoon-like style of the graphics of the original Sonic games. (as opposed to the Sonic Adventure style)
On the other hand, I think the game would be slightly improved if it used 7 direction sprites, (the other being top) but this is only a slight unnecessary improvement.