Okay, a slight update.  First off, the warp engine glows.  I took a look at the texture and noticed that...well, it looked splotchy.  So, I went in and fixed it, hopefully the color is still the same, and I made the circular thing on the top of the nacelles a little bluer.  Second, I brightened up the impulse engine a little to try and match ST4, I don't know if it's right or not, but oh well, it at least looks better.  Here's a comparison shot, left is old, right is new.
BTW, Dr_McCoy1701A deserves a few cookies for his assistance!