I don't understand why the drawing of your tiles needs to involve the delta value for every single tile. Can't you just use the delta to calculate the position of the tile row at the top of the screen, and then to draw all consecutive rows you add an integer value to that. ...... cus I think maybe it's just a matter of floating point numbers not being totally accurate, which may be causing the gaps. Have you tried using Doubles to see if that removes the problem?
As to the mesh idea, the concept is that basically instead of defining triangles you define strips of triangles and since the vertices are shared the API is able to take the adjacent triangles into account when figuring out antialiasing etc. However, this only applies to strips of triangles - what happens when you have a horizontal strip and you get to the end of a row and then you turn around and start a second row going back in the other direction? There is a gap between the rows. The triangles on the top row are not connected to the triangles on the second row, so surely you will still get the same artifacts vertically if not horizontally?
As to the mesh idea, the concept is that basically instead of defining triangles you define strips of triangles and since the vertices are shared the API is able to take the adjacent triangles into account when figuring out antialiasing etc. However, this only applies to strips of triangles - what happens when you have a horizontal strip and you get to the end of a row and then you turn around and start a second row going back in the other direction? There is a gap between the rows. The triangles on the top row are not connected to the triangles on the second row, so surely you will still get the same artifacts vertically if not horizontally?