Nitpick wrote:
I add +1 to the choir. To really make them sparkle, you would have to redo all scale giveaways. I'm thinking the rivets need to be replaced with small scale variants for one thing. Huge amounts of fiddly bits would probably be beneficial too...
Removing all the rivets would be a lot of work, but could be done. Personally the biggest things that makes those bastion towers stand out as not looking epic scale are the viewing slits, I'd have cut them off and filled in the holes or replaced them with something else for sure.
40k defence lasers can look a lot like giant lascannons though, so using 40k ones in epic can be appropriate rather than out of scale. As can be seen from the much larger again laser cannons on the Macragge's Honour (the Ultramarines Legion flagship in the recent HH graphic novel):

On the subject on large scale scenery I'd love to see someone having a go at making one of the 
eagle drop landers from the cover of the previous IG codex, it's pretty huge with hundreds coming down it's ramp at once and a nice eagle wing design. Probably more more scenario games or huge tables though as it'd cover too much of the table for a regular game.