Is there a mod that increases the view distance of neighborhood decorations so that you can see decorations placed at the farthest corners of the neighborhood while you are loaded in a lot? I know there are in-game settings where you can increase this distance, but it does not increase it by that much.

There is a cheat which increases the visible lot skirt view but I wouldn't recommend it. It can cause real graphic problems.

The sky fix does help with neighbourhood borders: http://www.modthesims.info/download.php?t=569032

To increase your view distance to the end of the neighborhood you must use this cheat:
uintProp lotSkirtSizeIncrease 120

And in order to see flora in the distance:
boolprop dontMergeNHFlora false

You can also turn off the fade distance in the settings so you can really see all objects no matter where your camera is positioned. Also sometimes objects are not showing up even if you are not close to them. So turning it off completely helps.

As already mentioned you should use SkyFix to see what's behind the invinsible neighborhood 'walls'. You will be able to see stars and other sky objects that Maxis screw up in the Seasons EP. Also with SkyFix you can place horizon and cloud objects in your neighborhood which then can be seen from lot.

To be honest, I never had a problem with the lotSkirtSizeIncrease. Everything works fine, I can see all objects in my neighborhood. No graphical glitches or crashes. It goes not get laggy, the only thing that laggs in my game is the actual lot.

Thanks Bob Newbie. "boolprop dontMergeNHFlora false" is just what I was looking for! Also Thanks Maxon for the link to the sky fix mod. I solved another problem I was having.