the gurus please correct me, i read somewhere saying that it is not really recommended/not necessary to use polarising filters at high altitudes. since u r going to Nepal, a country that is well over 1000m in altitude, is there still a need for a polariser at all?
Light usually falls in symmetrical waves moving in more or less straight lines. However, upon hitting objects like dust, water vapour or even grass and bodies of water etc, it disperses and the waves go nuts, fraying in different directions. This causes loss of colour saturation and unwanted glare and reflection. Polarizers are generally shaped in such a way that only the original waves and not the dispersed ones can pass through and to your lens, so colour is more saturated and glare is cut off. One of the main effects is that the sky will be very blue, because blue light tends to be scatter more easily due to its shorter wavelength. That's why the sky is never really super blue on a very bright, glaring day.
At high altitudes, the sky is already deep blue / violet in colour as more light of this wavelengths is visible at higher altitudes. It is mainly absorbed by the time it reaches lower altitudes. (same reason, because of its shorter wavelength) The effect of a polarizing filter will make the sky even darker / over saturated. So you get weird dark blue / purple at best, completely darkened out sky at worse.
What would be really useful to get is a good haze filter, because it tends to get reather hazy at high alt sometimes. The B+W ones are pricey, but well worth the money.
I don't know what camera the OP is using, but my $0.02 worth is this, after spending hundreds, or maybe thousands of dollars on your camera and lens(es), it does not make sense to spoil the whole set-up by getting a cheap and lousy filter. You image quality is only as good as the weakest link in your system. So, no point having the most expensive kit in the world, but getting a dinky $20 filter that causes vignetting, light fall-off and all sorts of other problems.