It all depends on how much you are going to be out in rain, and what kind of rain that'll be.
If you are going to be mostly in cities and towns, your needs will be much more modest than if you were doing long hikes in remote places even in a storm. October in Scotland can mean serious rain at times, so it's worth being prepared - but of course one can't predict the weather months in advance.
I'm leaving for Scotland tomorrow (the extreme north of Scotland, actually). We plan to do some hiking, so we're bringing the matching Goretex jacket and pants (and hat) - yes, the expensive stuff from REI. Also warm (non-goretex) gloves, too, and good, waterproof hiking boots - don't forget those.
I live in a place that's known for rain, and long ago I learned the value of good rain gear (when I didn't have it). If you're going to be out in serious rain, you really will appreciate having serious rain protection. It doesn't have to be high-end Goretex (but that's sure nice when you need it). If you're just dashing between buildings in cities or towns, your needs will be different.