I can't speak to an worldwind trip, but I can share some things that have helped my family with being able to afford things that we'd never thought possible.  Here's my situation, 1 income, 1 mortgage, 1 carloan, 1 student loan, 1 wife, 3 kids.

The first thing we did was set up funding goals for all our important categories, and then compared those against an accurate estimate of our monthly income. I get paid on a biweekly basis, so we used 2 paychecks, because that is all that we will reliably have each  month. Then we rounded the figure down to the hundreds place.

We have a big family trip coming up in August and we've been saving for it since last August. We set up a wish-farm category with the total estimated cost of everything for the trip (rounded up of course) as the goal, and the due date for the month before the trip. That gave us the monthly amount we needed to save for it.  And we made sure to include this when totalling our budget goals

Unfortunately for us, we discovered that our goal was several hundred dollars above our cashflow. We hadn't recognized it before because category goals gradually had crept up.  After this we looked at every category from the top down and asked ourselves if we could become more frugal, or even eliminate things like subscription services.  After that sobering look we were able to reign all our categories and eliminate wasteful/unnecessary spending. They are now a couple hundred less than our income.

It was sobering and some of it was painful, but after a month we realized that we are just as happy, maybe more, being more frugal. And the benefit of that all is that we now have a clear goal for the big trip and the monthly budget needed for it is much easier to swallow.

I did some quick back-of-the-envelope estimating, airfare for 4 from Australia to Ireland is probably about USD 5,000.  Assuming you'll stay with your friend, adding on 300 for groceries, and 800 for excursions. Gives a rough target of USD 6,100.  Spread that out across 2 years and it is about USD 250 each month.

Our family did the big budget realignment I described above a couple months ago, and in full honestly I don't even remember what we were spending all that extra money on, so we're clearly not missing it. :)  We were surprised how easy it was to adjust after the initial discomfort of budget belt tightening.

Chrissy said:
The Late Heavy Bombardment  Slow and steady is definitely the way to go! But I think you'll be there sooner than you think, especially if you're able to evaluate purchases through the lens of "Would I rather put this money towards my trip?"--I've found that to be very powerful. (snip)

 Want to add my emphasis to what Chrissy  posted  here.  It is exactly what I discovered myself, much to my astonished surprise.  After 4+ years of using YNAB I can summarize my progress as miraculous.  When I add up all the funds I used to live on, eliminate debt, help a relative in crisis, buy a car, build up a 7-month emergency fund, invest for retirement, and make some big necessary infrequent purchases, the numbers seem to exceed my income entirely.  I would not have guessed I would come this far this fast.  There really is something quite special that happens when you keep all your categories in front of your face all the time. You start adjusting your spending behaviours and tucking a few dollars into those special categories.   Those far-off-in-the-future wishes don't get forgotten in the daily day-to-day spending because you choose to include them in your category list. 

nolesrule said:
I've had close friends that have moved away. We don't go out of our way to make trips to see them, but if we can find multiple reasons to be in the area, we will include visiting them as one of the reasons to travel.

 Been there.  I've got relatives who live on the eastern end of Canada, and they seem to think that airplanes don't travel west, or perhaps it's cheaper for us to travel than for them. "It's cheaper to vacation in Florida or Jamaica than to fly to western Canada," they say and this is intended to excuse them from attending any family events in the west.  Perhaps they don't realize it's equally cheaper for the family in western Canada to go to Hawaii than to fly to eastern Canada.  The onus has always been on the western relatives to travel east for all family events, but for the eastern relatives to be excused due to cost.

One idea comes to mind, however, and that is for both the OP and the friend living in Ireland to meet halfway for vacation:  there must be some mutually attractive destination vacations in Malaysia, Thailand, Vietnam, Dubai, India........  Assuming that meeting up again is of equal importance to both people and not only to the Australian-based friend.