If you shoot this sort of thing in that sort of light all the time, and especially with that film, I would learn how to mask your negatives for printing.
For now, just make sure you are always exposing the foliage properly, and work very hard on your printing.
Also, keep in mind that overcast days are "blah," and there is not a lot you can do about the quality of natural light. It will be flat. An overcast day with the sky in the shot is one of the hardest photographic situations to print. You need enough exposure on the neg to get the color and density of the things on the ground right. However, with the sky also in the shot, you are facing a composition with a very high luminance range as well. You need enough contrast and saturation on the Earth-bound subjects, so any underexposure for those areas will generally work against you in that way. So, in this situation, you are double fracked. You have a very flat quality of light and a very wide luminance range. Either one on its own is relatively easy to deal with, but combined, things are very difficult, and you must rely primarily on your printing skills.
Graduated filters are fine if your subject has a perfectly straight dividing line between the dark parts and the light parts. (I think I may have taken only a handful of pictures in which this is the case and I did not want a great difference between the two to be evident, ever.) Otherwise, it can easily look like a bad burning/dodging job. If I was going to to a bad burning/dodging job, I'd rather do it on the print than do it directly on the irreplaceable film.
As i said before, I'd learn to mask. It'll be a great way to get the contrast, density, and saturation you want on the Earth-bound objects, while dramatizing the skies.
You can also do a dual scan HDR type thing. Try Hybrid Photo dot com to talk about that, though.
Polarizing filters will not help you here. They are about the farthest from what you should use in your case. They will either make the "blahness" worse, or do nothing at all.
P.S. If you are not using color correction filters in camera on overcast days (or in any color temperature significantly distant from the area of 5500 K), it can help to give negs extra exposure to make color balancing easier. With color film, you are actually exposing multiple images at once, stacked in layers; each one is sensitive to a certain part of the spectrum. You want to expose so that the least sensitive of the color layers in that light is not underexposed. If you don't, you can lose detail and texture, and make color balancing difficult if not impossible in the low tones of the image.