I guess if you're looking for things to add - its gotta be about architectural detail, first and foremost. You can pile a lot more architectural detail in JA than they could back in the days of GoldenEye - so take advantage of that. The hard part is keeping that Egyptian Temple look intact, so maybe find some good source material, shots from actual Temple interiors might be a good place to look. Your stock architectural detail things; pillars, supports, structs etc etc will probabaly suit in some places. Little details like maybe collapsed stones and holes might work, maybe some scrub like vegitation too?
Good luck, I'd like to see an updated GoldenEye temple
My personal favourite GE MP level would have to be Bunker I think...Complex and Facility were excellent too.