Maintaining relationships with aging parents on another continent

It has become clear to me over the last few years that being an expat means having your heart in two different (at least) places.  For me, I have my family, including my oldest son, and parents and sisters, in the States and my spouse and newer friends here.   Skype works relatively well, but I always feel I am dividing myself between two different continents in the connections I am trying to form and maintain. 
To add complication to this, my parents are aging.  They are both in good health, but they are becoming less mobile.  I have, in the back of my head, the magic number of ‘at least once per year’ as the number of times that I will see my U.S. family.  That feels woefully little, when one considers that this is a lifetime decision, not just a temporary one.  When one makes the decision of how often they will see their family, then one must save up the funds and vacation time to make that happen. Originally, I thought that I would fly my family here since that was cheaper than all of us travelling to the U.S., but it became clear that that wasn’t entirely feasible for various reasons.  Also, my father has announced that he does not think he will be making any more trips to Europe in his lifetime.  He has the money to do so, but travel seems physically harder and harder on him and his wife.  This pull to be on two continents at once creates a kind of a conflict inside.  Complicating this is the fact that my family in Denmark does not really want to spend all of our vacations in the U.S. (and particularly not in Texas!).  This is understandable but it only adds to the conflict we feel.  I am grateful that I have ample vacation time in Denmark, but it still never is enough to maintain loving relationships on both sides of the pond.
Many of my clients seem to have similar conflict.  Some of them have parents who are not well and cannot travel at all.  Sadly, a colleague of mine just had her mother die of cancer, in New Zealand.  She was not there to wish her mother goodbye.  Complicating everything was the fact that flights to New Zealand are expensive and exceedingly time-consuming.  It’s not humanly possible to make a quick trip to New Zealand on the spur-of-the-moment, when a medical crisis has afflicted a loved one.
For my more mobile family members, one solution has become to rent a summerhouse somewhere in Europe, in the summer, and invite them to come, with no charge for boarding.  This makes a yearly European vacation nearly doable, and has us assume part of the burden of cost for the rest of my family.  It’s fun, and it’s a ‘win-win’, in many ways.   Two summers ago, we rented a lovely place on Tinos, Greece, and paid to have it for three weeks.  Many members of my family came to visit and we made some exquisite memories.

It dawned on me that this is an important issue and I endeavored to find some information about long distance relating, in particular with aging parents.  There is almost nothing academic, though there are a few essays that I found.  One I will share with you here.  It strikes me that this issue is going to become more relevant, in our increasingly globalized world, and that we should share with each other strategies we learn to increase our sense of closeness to our birth families.  Feel free to write me or to comment here with your thoughts and ideas about this topic.