Presentation is everything. If you've spent alot of time working on something it should be framed. The base itself doesn't have to be expansive. Even if it's only 1/4" wider all around it will frame the piece and give it its own space.
If its on a base, you can move the base around without having to handle the model.
If you are going to a show, watch the way models with bases get handled as opposed to those without. Its really opposite what you might think. The ones with bases get slid aside, picked up and moved, bumped etc. The models with bases are treated almost as though they are taboo to touch. If they are handled then there is less likelyhood of it being damaged or marred.
Judges will tend to "judge" the pieces on bases over those that aren't. Maybe it's a carry over of -
if you didn't care enough about your model to "frame it" why should I...?
If its on a base, you can determine what best off sets the color of your vehicle or how it is seen. If you put it on a base or ground material that enhances your model then it is not as harsh a picture as on a white table cover or cloth. (I'm not sure if you guys catch me on this one, but its like putting a red square on a white background as opposed to a black one. Same color red, but you will perceive it as a different color becuase of your eye's ability to see contrast and compliment. Kind of like when they would put red meat on green trays in the grocery store. It just looked like a better piece of meat because of it. Which btw they can't do anymore)
Even if its a plain base its still better than none. It allows you to control to a certain extent the way your model is perceived.
Mike
"Imagination is the dye that colors our lives"
Marcus Aurellius
A good friend will come and bail you out of jail...but, a true friend will be sitting next to you saying, "Damn...that was fun!"