Not sure about the grain part... but someone had a pic a couple days ago with a warming polarizer and it really brought out some nice tones IMO.
There are also ways to adjust your camera settings for more vivid colors if you are shooting in JPEG, and the cloudy white balance setting seems to boost it a little when shooting outside. It seems like you are talking about more of a boost than this would do though, so it might even be Post Processing. Can you link to an example of what you are talking about?
An amber filter will give you warm, rich tones. It will make grain and wheat , or long grass, seem warm and yellow. If you want it to look "grainy" just reduce the resolution or bump up the ISO, or use a filter in Photoshop. POL filters can also make the light seem warmer.
vibrance and grain can both be enhanced or added in post-processing. personally i would shoot as you normally would but in raw (if you don't already) and adjust it all later, that way you are working with a clean slate and can alter it to your hearts content.