But there are some elements that I can cut down on, from flying direct to carrying my reusable cup, and lots of tiny little changes you can make in terms of wardrobe:
It makes no sense to have a load of stuff that you only use for one week every year, so the key is to cut down, share and choose more versatile garments...of course the same start from what you already have idea applies which in my case is:
6 pairs of ski socks, 2 pairs of thermal bottoms, one thermal long sleeve, a merino short sleeve, an air trapping jumper, ski trousers, a 2 layer ski jacket, a neck warmer, a head band a woolly hat, goggles and ski gloves. (all pre-cutting down decision)
The only thing I don´t own is skis and boots, but given that you can rent them cheaper than the price of checking them in on the flight, and it means you can have the most up to date version there is really no need to have your own set.
While I would be comfortable with borrowing everything else (or in this case since I own it all already, lending it to others) I understand that some people wouldn't be comfortable with borrowing socks or thermals.
So the first thing I would say is you need less than you think, you could even get away with the one pair of socks and bringing a bar of soap with you and washing them out in the evening. The other thing to note is that just because they are ski socks doesn't mean you have to be skiing to wear them! I have been wearing mine inside my boots from November to March every winter...some of them are actually even wearing out!
The next thing is thermals, which if you aren't happy to borrow, you could just replace with a similar item, winter pajamas, leggings and t-shirts, there is really no need to buy something specific if you have something at home to do the job. I do already have some stuff, so I try to get wear out of them when I am in Ireland too. My cousin used to wear hers on the the way to work to keep out the wind at the bus stop, and I've been known to use them as an underlayer if I am going somewhere cold, or planning to spend time outside. I am probably not getting as much wear as I should be out of the thermals I own, but I think the key is to try and keep them to as few as you can, so you don´t have multiple sets sitting at home most of the year doing nothing.
Your ski jacket could double as your winter jacket (and if it comes with the 2 layers that zip away from each other can be even more versatile) if you choose it well. Sadly I am not a huge fan of mine, so it doesn't get much wear, but if/when my down jacket and rain jacket need replacing I will start using it for outdoorsy activities (of course the dream is to have one that you would be comfortable wearing in the city too, but you have to work with what you have).
When I bought my ski scarf originally (maybe around 2005) I thought that a normal scarf wouldn't do the job (I had heard horror stories of chair lift strangulation), but now I know it really is not required, and you don't really need a separate hat either!
Ski pants are a tough one, borrowing or renting is really the way to go, because there isn't really many activities that require them in Ireland (although I have been known to sport them when it was particularly cold). I suppose looking after them, lending them where you can and using them for as long as you can is the best you can do.
Googles again are not very versatile, so unless you only plan to ski on nice days where sun glasses will do the job, borrowing or renting is the way to go here too, and failing that keeping them safe from scratches and extending their life.
So the key with ski gear is, borrow and lend, get as little as possible, substitute with more versatile alternatives, and use what you have as much as you can.