I think it's important that the ground tile contains a lot of eye candy in it's pattern, while the walls are all about adding depth to the equation...and if posible those ground tiles one floor above the playing ground should NOT have the same texture as the ground, since they're not playable.
I think that's a wonderfully logical rule. I totally agree. The "fun-factor" in a game is an abstract element, and nobody can clearly define it, or create a failsafe recipe for perfect gameplay fun every time. So, violoating little things like this, like what Conceit mentioned, detract from the game's fun because now your distracted with mundane things like trying to figure out what's out of bounds, etc, creating the opposite of fun - frustration. We've all played games that nickel-and-dime the fun away until it all that's left is annoyance.
I would like to cast my vote on the contrast-eye-bleeding-too-much-brightness issue - Helm has the right idea, yet ptoing's edit is the one I strongly favor.
Btw madPXL, the 3D world you've created is outstanding. Very cool style!