It's all about balance, when you can tell its a CGI shot, then it's probably went too far. If we are going to stick with one Biomech alien, it better be one hell of a script. You can't really get better than alien.
Unless they start with one and expand the egg morph into the second half of the movie, that might work out.
You know they might even go way out there and not actually show the full grown alien and just have a tale about the eggs. Although that would be a very "Ballsy" move.